The American civilization in Thrones and Patriots are actually Nephites and the game creators are secretly Mormon.That would explain them existing during the ancient age when doing a Conquer the World campaign.
Rise of Legends takes place After the End.Our future weapons drastically altered the very laws of physics. This did not end well for everybody.
The American government in the Thrones and Patriots Cold War campaign are controlled by radical extremist.In the many playthoughs that this troper had playing the Cold War Campaign as the Soviets, if part of the US mainland is in my control by the time that Defcon 1 was reached, the Americans will NUKE the parts of their own country that are under Soviet control. In fact, they will give it even higher priority then major cities in Russia. This doesn't happened if the situation is reversed (The Russians will never nuke their own country unless they ran out of places to nuke). My only explanation is that the US government in the campaign is under the control of an axe crazy extremist.
Romans in the later eras are Italians.