Here I will talk about a lesser known episode of the First War, one that was revealed in Chronicles II but who may not be known by those who have only played the games and/or read the novels, it's the war in Stranglehorn Vale.

After arriving on Azeroth and beggining the war with the kingdom of Stormwind the Horde began to explore lands south of the Dark Portal and of the Swamps of Sorrow where they had set their main bases, and of course they quickly discovered the lush and savage jungles of Stranglehorn Vale.

Killrog Deadeye and his Bleeding Hollow clan who used to live in Tanaan Jungle were of course immediatly drawn to this region similar to their homeland on Draenor and sought to make it their new home and so they led the Horde expeditions in the Vale.

Of course this wasn't counting on the presence of Stranglehorn Vale's sapient inhabitants, the Jungle Trolls who were still recovering from their disastrous attack on Stormwind where Medivh decimated them with his Guardian powers over a decade ago, and had no intention of letting anyone take their home from them. Against these new invaders the Gurubashi rallied all the Jungle Trolls tribes in the Vale and fought back against the orcs.

The war between the Horde and the Gurubashi Trolls was particulary violent and savage, both belligerents were particulary vicious and bloodthirsty foes and each were used to fight and survive in hostile environments, with the Bleeding Hollows having dealt with Sabrerons, Arrakoas and especially the Primals in Tanaan Jungle.

However the Gurubashi, despite still being weakened from their loss at Stormwind City, if they had they managed to get the advantage over the orcs, despite being inferior in numbers their perfect knowledge of the jungle and of guerilla warfare allowed them to inflict many losses on the orcs who were ambushed on all sides and failed to hold the land against their foes.

Upon hearing about the losses in Stranglehorn Vale without any real gain of land, Black Hand decided that it was enough and ordered Killrog and his troops to retreat from the jungles and to join back the fight against humans, saying that the Horde would deal with the Trolls later.

The Jungle Trolls did not pursue the orcs beyond their jungles, as they still didn't have the numbers to match the Horde outside of their homeland and the advantages it granted them, though they remained wary and prepared for another Horde invasion. While this episode didn't have any big impact on the war with Stormwind and the Second War it showed that the Horde wasn't fighting just the kingdom of Stormwind during the First War, and it explains partially why the Gurubashi Trolls unlike their Forrest Trolls cousins and the Darkspear Tribe have always remained hostile to the Horde.