I chose primarily Austro-Hungarian and outdated British weapons for no reason other than style. Personally I don't mind what kind of weapons your armies use, so long as they fit the bill of being a slightly older rifle. They could be knockoffs or bought in dribs and drabs through the black market, doesn't really matter. If you want to be 100% accurate, then sure go for it. But no-one will be forced to use a certain weapon purely because of historic accuracy.
... Alright, common sense here too. No assault rifles in 1910.

Sven, I'll make a decision when its 100% complete, but it looks good so far. Very populist.