When Titans lose their military value, what form of deterance will a 3rd world, technologically inferior, sparsely populated island nation have?

Armin talking and telling Eren to stop misses the point in the entire rumbling. The rumbling is a form of deterence, the initial plan was to discourage other nations in invading Paradis for a definite amount of time. However, Titans in the future will become obsolete, so their form of deterrence has a time limit. Which goes back to my first question, if Armin and Eren talk it out and convince people to stop killing Eldians, what's their plan B? The reason why Eren acted on his own and initiated the rumbling in its full scale is because the future of Eldians is uncertain, there are too many what ifs for the security of the Eldian people.

Assuming that people become saints, harbor no violence and ill will to the Eldian people for slaughtering them in the past and the present, what then? Will everyone just hold hands and sing kumbaya? Because that doesn't happen with humans, especially between nation-states.

Yes, genocide is clearly wrong but in an international arena which Mr. Braus put it as "a forest where people fight for their lives" there is no such thing as trust, friendship and alliances. Those things only exist between nations in order to pursue their own interests. It's something we call in international relations as realism. Paradis had no choice, again with the reason that Eldians and their future lives will be constantly at risk and the same goes for all non-Eldians. It is an unfortunate consequence of this world that Eldians are beings which are literally walking WMDs (Weapons of Mass Destruction).

Unless there is a solution to end racist/populist politics, titan powers, upholding global peace and stopping imperialist conquests, there will be no certain happy ending. Which I hope Isayama-san will address.