Overpopulation is not a thing. We can grow the world's food in an area slightly larger than Texas. Humans barely cover 0.2% of the earths land (assuming 1/4 acre each). The only places that are overpopulated are cities.
I think they went wrong when they let anyone vote, even people that don't have skin in the game.
Personally I think they should only let net positive tax payers and veterans vote. I also think there should only be one vote per household and if you are single you count as part of your parents household.