Jon spends all of ADWD stationing men all over the Wall at different castles. Some are Night's Watchmen, some are Free Folk, some are Stannis' men, borrowed to inflate the ranks.

Bowen Marsh, among others, complains that Jon has set up a potentially sticky situation:

When he conferred Oakenshield on Tormund Giantsbane and Queensgate on Morna White Mask, Marsh pointed out that Castle Black would now have foes on either side who could easily cut them off from the rest of the Wall.

How true is this? How right is Bowen about strategic imbalances here?

I believe, following the Jon Snow murder, we're going to see the Free Folk and the Night's Watchmen divide again; Jon was the glue holding the two together, and now he's gone. But since Jon settled them in various castles along the Wall, we need to work out the strategic layout of each of these positions in the event of such a split.

To start, I'm going to argue that in typical GRRM fashion, the lede is being buried here. After breaking down the state of the Wall at the end of ADWD, it's not so much a matter of Castle Black being surrounded, it's that the entire Wall is going to be split into two parts... with the Nightfort in the center. Coincidence? In this case, I don't believe in coincidence.

The Wall Diagram

I hope this makes sense visually, because I needed a visual.

This is a diagram of each castle at the Wall at the end of ADWD. "NW" indicates this castle is going to fall on the side of the Night's Watch in a hypothetical Watchmen/Wildling divide, and "FF" indicates this castle will fall on the side of the Free Folk. "UM" is going to stand for unmanned; that castle is empty. Special cases will get asterisks that I will explain in detail later on.

From west to east:

1.UM*—2.NW[Shadow Tower]—3.UM*—4.NW—5.UM—6.UM—7.NW—8.[Nightfort]....

....9.FF—10.FF—11.[Castle Black]—12.FF—13.UM—14.FF—15.UM—16.FF—17.UM*—18.FF—19.NW[Eastwatch-by-the-Sea]

* This castle is never/rarely mentioned in the main text. The wiki says this is garrisoned, but there is no evidence for that in the main text, so I am assuming they are unmanned.

This is the point: except for Castle Black and Eastwatch—which I'll get to soon—every castle lined up to fall on the side of the Night's Watch is west of the Nightfort, and every castle primed to fall on the side of the Free Folk is east of the Nightfort.

Since the Nightfort is going to be the seat of King Stannis and Queen Selyse, their home base will be geographically attempting to do what Stannis’ cause is trying to do politically: negotiate stability with the Night’s Watch on one side and the Free Folk on the other.

Castle Breakdown

1. Westwatch-by-the-Bridge

This is never mentioned in the main text, and only appears on maps. This is potentially garrisoned by Night's Watchmen, but there is no strict textual evidence.

2. The Shadow Tower

One of three that’s manned prior to ADWD, so there’s a history of intra-Wall politics already at play here.

Denys Mallister cast the votes of the Shadow Tower watchmen for Jon Snow at the end of ASOS, but their relationship has been slightly more strained over the course of ADWD; Mallister regularly requests more men to resist the threat of the Weeper, but Jon has few men to spare. 

As of the start of TWOW, two of Jon’s friends are at the Shadow Tower, Halder and Toad. Halder carved the Ghost pommel on Longclaw, and both Halder and Toad are part of the group that tries in vain to remain close friends with Jon once he’s Lord Commander. These two might fall on the side of the Night’s Watch if the lines of conflict are drawn there, or they might remain loyal specifically to Jon if that remains an option for them.

Additionally, the Shadow Tower has ten wildlings that Jon sent over that he collected from Mole’s Town. While these are young boys and untrained, they are likely to either break for Jon or for the wildlings, depending on where the lines of conflict are drawn; in any case, they are unlikely to remain loyal to the Night’s Watch in Jon’s absence. However, being so outnumbered, I don't know how much impact they will have.

Additionally, this is explicitly and directly relevant for a potential conflict about the Wildlings crossing—Mallister says he believes the Weeper is gathering a host to force the Bridge of Skulls again, and threaten the Shadow Tower. Bowen Marsh, at Castle Black, was injured at the previous attack at the Bridge of Skulls, and the Weeper has very visibly and brutally killed three rangers and returned their heads on spikes to Castle Black. Tensions will likely be especially high between Free Folk and Night's Watchmen with the possibility of the Weeper attempting another assault.

3. Sentinel Stand

Like Westwatch, this is never mentioned in the main text, and only appears on maps. This is potentially garrisoned by Night's Watchmen, but there is no strict textual evidence.

4. Greyguard

A fun fact about Greyguard: Jeor wants to man Greyguard during the events of ACOK, but Qhorin convinces them to garrison Stonedoor instead; as a result, Greyguard is unmanned when Jon, Ygritte, and the wildlings climb the Wall, and they descend into Westeros from Greyguard. 

This is also where Janos Slynt fatally refuses to go.

As of TWOW, Greyguard is manned with thirty men: ten from Castle Black, ten from the Shadow Tower, and ten of Stannis’ men. Following the death of Janos Slynt, Greyguard is captained by an experienced Shadow Tower watchman. 

Additionally, Jon commands that some of the free folk from Mole’s Town to be sent to Greyguard as needed, though it’s unknown how many are sent.

If there’s a divide in loyalties here, the captain of Greyguard is a Night's Watchman and, presumably, a loyal Shadow Tower man, so they may be ordered on the side of wherever Mallister falls, or his prior loyalty may lead them to break from their post and defend the Bridge of Skulls if necessary. There are also the 10 men from Stannis' forces, but it's hard to say what political influence they'll have.

5. Stonedoor

Jon intends Stonedoor to be manned by a wildling force: he settles the abandoned castle on Soren Shieldbreaker, who is meant to leave with the wayns as soon as they return from Greenguard; Borroq the skinchanger is to accompany him.

However... as of the last chapter of ADWD, both Sorren and Borroq are still at Castle Black—the castle, right now, is still totally unmanned. Both are present in the shieldhall when Jon reads the Bastard Letter, so as of the end of ADWD, they have not actually made it to their intended seat.

Othell Yarwyck claims that the woods around Stonedoor are filled with boars, and fears Borroq leading a boar army. While we have no reason to believe Borroq is as skilled as Varmyr in changing multiple animals at once, this is an interesting possibility to point out. Jon also notes that Ghost and Borroq’s boar seem at odds, so we may see Borroq get aggressive in a Wall fallout situation.

If this were manned, this castle would undoubtedly break away from the Watchmen faction, either joining up with a pro-Jon faction or else Tormund/a wildling faction. It would be outnumbered by Watchman castles on both sides, but it is potentially a defensible position. But that depends on how long Jon’s intentions hold following his death. If conflict breaks out right away, they may not make it to Stonedoor at all. 

Also, like other wildling commanders, Soren Shieldbreaker’s son is one of the hostages taken as Jon’s blood price for crossing the Wall; whether his son is at Castle Black, the Shadow Tower, or Eastwatch is unknown.

6. Hoarfrost Hill

Hoarfrost Hill is in a similar situation as Rimegate. In Jon’s final chapter, he intends to give this castle to a wildling commander. As of now, it's unmanned.

When considering it, Jon's suggestions are: Brogg, Gavin the Trader, the Great Walrus, Harle the Huntsman, Harle the Handsome, Blind Doss, and Ygon Oldfather, though most of Oldfather’s following is his family. Howd Wanderer is named but unlikely as a candidate because he walks alone. 

However, Bowen Marsh dislikes all of these suggestions as every one is, in his mind, a wildling criminal who deserves to hang. Jon dies before naming a party to move there, and thus it is still unmanned as of the very end of ADWD—though intended to have been a wildling post.

7. Icemark

Icemark appears to be manned similarly to Greyguard; both were manned together with the same intentions. If they were dealt with the same way, Icemark similarly has a force of 20 Night’s Watchmen and ten of Stannis’ men. It’s not explicitly stated, but it is possibly the same split of 10 Castle Black, 10 Shadow Tower, and 10 of Stannis’ men. Like Greyguard, the Shadow Tower, and Eastwatch, Icemark has also received an unknown small number of the free folk recruited from Mole’s Town. 

Icemark is commanded by Bedwyck, known as Giant, from Castle Black. Bedwyck survived the assault on the Fist of the First Men, so he understands the very real threat of the wights. During the mutiny at Craster’s Keep, Bedwyck stayed loyal and returned—so it’s possible he’s not a part of this mutiny, either, and may be still sympathetic to Jon’s cause. However, he survived the attack on the Bridge of Skulls too, so like Bowen Marsh he’s also seen the worst of the wildlings. 

This castle will likely break for the Night’s Watch, though like Greyguard there is a potential for a 2:1 split if Stannis’ men don’t align with the Watch’s intent.

8. The Nightfort

Jon gave the Nightfort to Stannis and his cause to make it the temporary seat of King Stannis. Queen Selyse is, so far, meant to be on her way to the Nightfort from Eastwatch. Currently, though, she's still at Castle Black.

Since this is a prominent location in a number of scary stories—and is the location of the mysterious Black Gate—I think there’s a high likelihood we haven’t seen the last of this location and that we may see some more action go down here. 

Jon had sent Othell Yarwyck to oversee the repairs at the Nightfort to make it available for Queen Selyse to live in, and Queen Selyse arrives at Castle Black intending to make only a quick stop before continuing on to the Nightfort. 

As of Jon's last chapter, Yarwyck has returned to say that though the castle is still largely a ruin, it is habitable, and Selyse can move in if she would like. He also notes that the castle is very isolated from the sea, should Selyse want to leave. I don’t think that detail is included for nothing: if things go sour at the Wall, Selyse in the Nightfort is going to be blocked in with no escape but north and south. 

At the end of the ADWD, though, Selyse is still at Castle Black. Like with Soren Shieldbreaker, it’s hard to say whether she manages to continue on to her intended destination further west, or if her path will be derailed by chaos at Castle Black. If we presume she makes it to the Nightfort, then that will undoubtedly be a Stannis stronghold, if not then the castle will be unmanned. 

Note this: from here on out, the castles are more heavily manned by Free Folk.

9. Deep Lake

Deep Lake is one of several castles Jon intends to man with free folk, under their own command. We don’t hear much concrete information about this, but it is apparently manned as of Jon XI, potentially by Halleck, brother of Harma Dogshead. (If he isn’t here, then he may be at Sable Hall). 

Doubtlessly, this will break to whatever side the free folk break to, presumably with Tormund.

10. Queensgate

Queensgate is also manned by wildlings, commanded by Morna White Mask. 

Like Soren Shieldbreaker, Morna’s son is a hostage of the Night’s Watch as part of Jon’s blood price for crossing the Wall. Whether her son is at Castle Black, the Shadow Tower, or Eastwatch is unknown. 

Marsh points out that between Queensgate and Oakenshield, Castle Black is easily cut off by wildlings on both sides—a detail I doubt was included in vain.

11. Castle Black

This has a lot going on, of course. As of the end of ADWD, Jon has just been killed, and here's the issue: Jon has just spent the moments prior riling a host of volunteers to die for his cause... I think Bowen Marsh misjudged, because these are the worst possible conditions to make a martyr of someone in.

Following Jon's death, this is the situation:

Immediately following the crossing of the Free Folk in Jon XI, Bowen Marsh clocks that the Free Folk will outnumber the Night's Watchmen three to one. Some of these men have started to disperse throughout the Wall, but not much time has passed—most are still here, at Castle Black.

Even if the commanding force is the Night's Watchmen, the majority here are wildlings... and this time, there are other commanders at Castle Black. Tormund is here, ready to go to war, because Jon requested it.

As far as fighting men specifically: Tormund has 80 60 fighting men there, which he has brought back from Oakenshield. Soren Shieldbreaker has all of his people with him, because they were supposed to leave for Stonedoor soon.

In the Shieldhall, just before Jon's death, there are 200-300 men—and, as Jon notes, the Free Folk outnumber the Night's Watchmen 5 to 1.

All in all, though this is a Night's Watch seat, there are all the necessary ingredients to make Castle Black into the seat of the Free Folk; the numbers are on their side. And they're surrounded.

12. Oakenshield

Jon granted Oakenshield to Tormund Giantsbane, which is convenient: it's perfectly central for Tormund to lead from, should the need arise.

As of the end of ADWD, Tormund has returned to Castle Black with sixty fighting men, presumably leaving even more still at Oakenshield. This will definitely be a key stronghold for the free folk if conflict divides the forces at the Wall.

Like the other commanders drawn from the Free Folk, Tormund’s son is a hostage, located now either at Castle Black, the Shadow Tower, or Eastwatch.

13. Woodswatch-by-the-Pool

Woodswatch is mentioned only once in the main series, in ASOS, and once on the ASOS map. It is not mentioned as one of the garrisoned castles, so it is presumably empty.

14. Sable Hall

Sable Hall is one of several castles Jon intends to man with free folk, under their own command. We don’t hear much concrete information about this, but it is apparently manned as of Jon XI, potentially by Halleck, brother of Harma Dogshead. (If he isn’t here, then he may be at Deep Lake). 

Like Deep Lake, this will doubtlessly break to whatever side the free folk break to, presumably with Tormund.

15. Rimegate

Rimegate is in a similar situation as Hoarfrost Hill. In Jon’s final chapter, he intends to give this castle to a wildling commander. As of now, it's unmanned.

When considering it, Jon's suggestions are: Brogg, Gavin the Trader, the Great Walrus, Harle the Huntsman, Harle the Handsome, Blind Doss, and Ygon Oldfather, though most of Oldfather’s following is his family. Howd Wanderer is named but unlikely as a candidate because he walks alone. 

However, Bowen Marsh dislikes all of these suggestions as every one is, in his mind, a wildling criminal who deserves to hang. Jon dies before naming a party to move there, and thus it is still unmanned as of the very end of ADWD—though intended to have been a wildling post.

16. Long Barrow

I feel sort of certain that Long Barrow has to matter somehow because we’ve been following updates on it frequently throughout ADWD. Jon has manned it with entirely spearwives, commanded by Iron Emmett, and with Dolorous Edd as chief steward. 

Iron Emmett is a watchman who was first at Eastwatch and later became the master-at-arms at Castle Black. He and Jon have had a tense run-in before—in ASOS, Jon fails to recognize Iron Emmett’s yield and attacks him brutally while sparring. However, that doesn’t immediately seem to get in the way of his loyalty to Jon; Emmett is the one to hold Slynt down for his execution. On the other hand, perhaps this is another up-close encounter with Jon’s brutality. In sending Iron Emmett to Long Barrow, Jon removes him from his post as master-at-arms and replaces him with the wildling Leathers. In short, it’s possible that Iron Emmett and Jon are close, or it may be possible that Emmett has reason to resent Jon’s leadership. 

Dolorous Edd, for that matter, is a loyal and longtime friend to Jon who seems unhappy with his current station as steward to the women at Long Barrow.

If there is any kind of split in loyalty at the Wall, Long Barrow would be an interesting situation to watch: the commander is likely most loyal to the Night’s Watch, and might hold some particular loyalties to Eastwatch in particular, but the people actually manning the castle will likely split for a wildling/Tormund faction. Dolorous Edd might remain loyal to Jon, or might remain loyal to the Watch and side with Iron Emmett against the spearwives. I hope he survives. 

For now, I'm considering Long Barrow to break for the Free Folk, considering the disparity in numbers, but Iron Emmett could make a surprise angle here.

17. The Torches

This is one of the handful of castles that appears only in maps and is never mentioned in the main series. This is potentially garrisoned by Night's Watchmen, but there is no strict textual evidence.

18. Greenguard

Jon settles Greenguard with free folk under the command of Devyn Sealskinner. 

Like the other wildling commanders, Sealskinner’s son (or sons) is a hostage of the Night’s Watch now, either at Castle Black, the Shadow Tower, or Eastwatch.

Doubtlessly this castle will be loyal to a potential wildling/Tormund faction if there is a split at the Wall.

19. Eastwatch-by-the-Sea

Like the Shadow Tower, Eastwatch is one of the few castles manned prior to ADWD, and therefore one with a more-established political presence at the Wall. 

Cotter Pyke, the commander at Eastwatch, voted for Jon in the Lord Commander election. Since then, he’s had to host Queen Selyse prior to her departure the Nightfort, and apparently Eastwatch ultimately resented her presence, wanting to be rid of her and Axell Florent both.

Interestingly, Eastwatch has a lot of moving parts happening around it at the moment. 

As of the end of ADWD, Cotter Pyke has left Eastwatch with a number of ships, some belonging to Tycho Nestoris and the Iron Bank, in order to retrieve a large host of wildlings stranded at Hardhome, apparently a four-day trip away by boat. This mission appears to be a failure, with “dead things” in the woods and the water. Pyke’s boat is taking water, so we may or may not see him return.

Meanwhile, Eastwatch’s interim commander is Glendon Hewett, which troubles Jon—Hewett was part of the Thorne/Slynt coalition before Jon became Lord Commander. If there end up being two groups of Night’s Watchmen—those pro-Jon and those anti-Jon—then Hewett’s Eastwatch will certainly be anti-Jon. In addition, should it ever matter, Mance might remember Glendon Hewett for beating him up while disguised as Rattleshirt. 

Meanwhile, all of the goods, gold, and trinkets that Jon claimed from Tormund’s wildlings when they crosses is being sent to Eastwatch to trade, ostensibly to cover the cost of feeding the free folk, though more accurately as a cover for the debts Jon has already incurred with the Iron Bank. 

Meanwhile, the giants and mammoths that could not cross the Wall with Tormund (because the mammoths could not fit) have been sent around to Eastwatch to cross by going around the Wall instead. 

So, at Eastwatch we have the wildling’s treasures, the giants and mammoths, and any survivors from Pyke’s excursion heading home, crossing paths under the watch of anti-Jon Watchman Glendon Hewett. 

If Stannis’ plan goes as intended, then Justin Massey should be crossing through Eastwatch as well on his way to Braavos—assuming he is not waylaid on the way by chaos at the Wall. 

Additionally, Melisandre suspects that one of her visions of a tide of blood around a tower is about a tragedy about to befall Eastwatch; this may or may not be the case. 

Whether or not Mel is right, Eastwatch is just waiting to turn: the giants are approaching from the North, the riches of the Wildlings are approaching from the west, just waiting to be reclaimed. If Cotter Pyke never returns, then their forces are forever depleted; if he does return, then he brings with him enough wildlings to overwhelm the Night's Watchmen. Best of all, their leader is Glendon Hewett, a man who beat Mance and kicked Jon in the ribs—in other words, someone who might die without the Jon (or the reader, perhaps) feeling too badly about it. I predict Eastwatch might fall to the Free Folk if the story necessitated it.

In Conclusion

It's almost a perfect split with the Free Folk on one side of the Nightfort and the Night's Watch on the other—and I don't think that's a coincidence. It's almost as though this is being hidden from us, because it appears, at first, as though it's slightly less stark of a divide, but that's illusory: Iron Emmett's presence on the East is really a castle of the spearwives, and Soren Shieldbreaker's intended castle on the west has yet to be actually settled—as of now, it's unmanned.

As things actually are, it's a killer split, with Jon martyred and the Free Folk in command of the eastern half of the Wall, the Night's Watch on the west, and the Nightfort in the middle.