What are good costumes for a war movie?

You don't need uniforms to make them look like uniforms. As long as the clothes are uniform (sorry, I couldn't resist) and the same. You can get berets and make sure the evil army blouse their trousers into their boots. As far as militia goes, black, green, brown, ripped and dirty t-shirts are good. as for trousers I know that old military uniforms are pretty cheap in army-navy stores. But if you can't take that route, just regular dark jeans would be decent.