Well, this ain't realistic. Anyway, as RL shows, you can draft as many troops from as many countries as you want, but quality goes down the pan!
It makes good cinema and lets Lucas play with sci-fi stuff as he pretends he's an expert on robotics and cloning. Heck a single suicide bomber would wipe the senate. 9/11 x1000 methinks.
I am the definition of your defeat.