I don't think you could do a Call of Duty for the Falklands war, since uhh, well purely for money reasons, most Americans don't even know there are group of islands called the Falklands, let alone there was a war. The Korean War? The weapons used were very similiar to WW2. Vietnam? No, just... no.

I think Infinity Ward will do another modern age game after CoD5, to be cynical, well they've killed Arabs and Russians in the last one. So this one would of course involves China or another Far Eastern power.