I'm making a situation where in the near future(5 year), the world is thrust into world war 3. The vast majority of the world's military is decimated, and it is to the point where any high tech equipment like planes, missiles, tanks, etc are being used in moderation. During the war, India and Pakistan launched nuclear weapons, which is causing a semi-nuclear winter, leading to mass famine. As a result, country start to fracture into large unified states(map included). However, due to resource crisis(drinkable water, agricultural land, oil, etc), the states are all constantly gearing up to attack, but this time, without the larger amounts of modern military technology that we see today. The New USA(need...better...names) has retain the majority of modern USA military equipment, but each of the region has managed to retain a good amount too, but all state are mainly saving it for defensive purposes.
But anyways, is that without as much modern technology, each conflict is fought relatively low tech, with limited air support, etc.
Since the conflict are literally vital to the new state's survival, the state will commit as much man power as needed to secure resources that they need to keep the country running.
Would it make sense to draft at a state-wide scale in this situation? Each state is extremely large, my quickly named "Western Socialist States" would have a population of about 54.423 million at the current time, a very large percentage would have to die to due to famine or something if it would make sense to draft like South Korea for example, where all men from 18-28 must do compulsory military service. But South Korea does have a population of 51.71 million, and if things were as bad as a go-to-war resource deficit, then maybe it would make sense. And I'm no tactical warfare expert, but I'm not convinced having armies with hundreds of thousands even be that useful, unless the military leaders were only doing frontal assualts.