everyone talking about "what if hitler kept the uk out of the war" keeps assuming that the uk existed in its own little pocket dimension completely separate from the rest of the world. britain for obvious reasons had very deep military ties with france, and even with the rise of the ussr germany never really dropped lower than public enemy #2. keeping the uk out of any conflict would have required avoiding keeping france out of any conflict as well, and basically the only way to do that would have been to completely avoid starting any sort of war at all.
United Kingdom