Follow up question:

How did large armies actually exist? I've read that there were armies large as 50k, 100k or even larger.

How could a population maintain armies like that? Considering that only males were in the army and also huge numbers of people died in battles. How did they recover?

It always baffled me that they could loose like 20 or 50k in a battle and then send in a new army. HOW?? Where did all the soldiers come from?