How would you even define 'overpopulation'? In the middle ages the population in Europe was fraction of what it is now, and yet still the were many wars. Still extant tribal societies in places like Amazon and New Guinea are even more warring, with higher percentage of casualties. And Russia's and Ukraine's populations were in decline before the war, and weren't pushing any thresholds in terms of number of people per km2(Russia is one of the least densely populated countries, Ukraine is in the middle of the pack) or some Malthusian limit in terms of food (there is overproduction of grain in Ukraine and Russia).

>Being poor is the result of the overpopulation

bunch of moronic bullshit. The Netherlands is much more overpopulated and somehow there is no war in that part of Europe.