America has contributed a lot to modern Britain, still, I do not believe the American people (90% of, that's not you) know of, or are grateful (that's the same for the American government) of the British contribution.
Thank you for realising this though.
Now; America was all for economy, their strength came from their economy. Large production was their winning factor, the majority of their planes were average but the few winning designs (B-24, P-38, B-29) all proved to be excellent and some of the best in the war, without British intervention. Late war, they were starting to get the idea in technology, even on the ground.
They were respectful of the lives of their troops, as much as you could be in war. Always willing to try new ideas, which is a brilliant stratergy (maybe Britain should take up that way of thinking)
Britain was always for technology, competing with Germany for years. Their economy was small in comparison to America, and made even smaller in the BoB. Their aircraft, and tanks (although few in number) were of mostly brilliant design. Some would argue they didn't care about their people (you should see, and read some of the missions people were sent on) but that attitude is still taken today, it is confidence in its own troops which makes them one of the best, if not the best force in the world. (No offence intended to the Americans but they always top the NATO ground force exercises)
Always trying to cut costs, during war and peace. Which results in keeping many designs for decades.
Russia; Russias doctrine was simplicity and numbers, which showed in their mass production runs and simple designs. It proved effective and with great loss of civil and military life by both them and their enemy. 16 hour working days for the factory workers, and suicidal missions for the army.
Shot by their own people as well. They didn't care for their people. Throwing out designs left, right and center but always needed Stalins approval. Helped greatly by the Christies suspension system (New Jersey, well done America)
Germany; Germany believed in greatness and supremecy, and they showed it. Technology was top notch, and many of the worlds modern technologies came from Nazi Germany, or from the Germans themselves working after the war. Even down to the finest touch they were about precision, and technological brilliance.
They cared about their people to an extent, and treat them well. A lot of internal rivarly prevented the German forces reaching their full pontential. Stopping projects that were quite clearly needed.
Japan; Good technology at the beginning of the war, but they were fighting a loss. Probably soon realised this after Midway. Their brainwashed people were willing to die for the cause, and the Emperor was willing to let this happen.
Out of the Jungle these the Japanese did not know how to fight, but served well in the seas, and air.