The United States (as well as Britain) managed to survive the war relatively undamaged.
the United States initially tried to remain neutral in WWII. However, after the Japanese attack on the Philippines, the US was drawn into the war. The disastrous defeat at the Battle of the Philippine Sea, in which the entire Pacific fleet was destroyed in a 'Battlewagon' fleet action reminicant of Jutland, forced the United States to reconsider.
Stalemate and cold war
The Bush Years
George H W Bush was elected in 1972 over RFK, with the "failed promise of Camelot" being RFK's legacy as well as fears of a political dynasty building up. Bush also accused Kennedy of being an appeaser, who in turn called him a warmonger. Bush would up the ante of the cold war with the Third Reich and Japanese Empire, trying to outdo them in every way possible (militarily, economically, technologically). He would also use a different tactic: trying to drive a wedge between Germany and Japan while their relations were souring.
The Americans would also give soviet partisans in the Urals new Redeye and later Stinger missiles. When one shipment of these was intercepted, this nearly started world war three, although both sides had the sanity to back down.
These policies were unpopular at home, with the American economy entering recession by 1975. Uralgate (a portmanteau of Urals and Watergate, where reports of shipments were uncovered) nearly got him impeached.
Today, America is one of the leading powers on earth, and is on an equal footing with the Greater German Reich in many ways possible (except in space, where the Von Braun Stations are masters of the heavens). Many economists say that it would be the most powerful nation on Earth by 2020, although that is normally said only in cabinet meetings to prevent it being a casus belli for World War 3.