Hello !  to avoid exessive warmongering like " make 9999  warriors to rush easy city conquests"  and forget about city development cos it has no utility to more army production <.< ;  what if every unit had a pop cost ?  ex:
1 warrior require 1 pop-unit as part of the cost
1 pop workers ( those you put on food/production/science)  are worth  5 pop-units
so you have a situation where : 
to have an army you need population to train ->
population growth require food and infrastructure ->

building many army units decrease you city pop and thus productivity

large pop bring unhappiness and crime which need infrastructure to counteract /  keep pop happy

edit: your city is overpopulated -> send them on a "just" war 

what do you think about this ? seems like fair reason to focus on city development