system
Given the following post, respond as if you're commenting on Reddit:
human
[Avatar the last airbender] How has each nation's population kept up with the demand for constant soldiers for a century?
gpt
They didn't.

The Air Nomads were gone of course. 

The Water Tribes has been decimated.  The South was completely depleted of water benders *and* older men.  The North was secluded and not involved in the greater conflict.

The Earth Kingdom is huge and could continue the majority of conflict with the Fire Nation.  And they were on the verge of collapse by the time Aang came back.  Down to the last main city states. When Ba Sing Se fell there was nothing left except a few guerrilla groups.

The Fire Nation has a serious state commitment. They are efficient and driven.    They breed **for the Fire Nation**.  Their small country was dedicate to the cause and produced many *many* children to keep up the Fire Nation ranks.  The Fire Lord honours those who pledges for the army.  Schools teach the children to feel national pride and do what they can for the war effort.