User blog comment:AndImBatman/A theory: New Black Ops II Zombies Storyline/@comment-5960038-20130113001715/@comment-3967954-20130124074205

CoD3 had Polish and Canadian forces, which was a change.

Anyways, the reason there's always American armed forces in CoD games is because all the development stuidios are based in America, so it's just downright easier. Easier to get voice actors, easier to know which sort of kit they'd use, etc.