Hitler mistimed his advance into Russia, caught in winter but eventually would have defeated the Russians if it were not for the USA. Our involvement divided and thinned Hitler's troops on multiple fronts as he was forced to prepare for a channel invasion as well as renewed pressure on all fronts.
Before we entered....
Russia was in full retreat, scorched earth policy.
He had the Brittish pushed out of Europe on retreat in Africa and basically cutoff isolated on their island.
Japan brought the full weight and resolve of the USA into the war.
They all would be speaking Deutsche and China would be speaking Japanese if it weren't for us.
What a lot of people did not know is the US gave the Russians tanks, howitzers, aircraft to help them fight off the Germans. Without it, the Germans would have won! American pilots also, flew for the RAF and fought the Germans over the skies of the UK and Europe! Sad the disrespect they showed President Trump during his visit to the UK and Scotland while, he gave Merkel, Macron and May warm welcome's during their visit to the Whitehouse and USA! Yet, President Trump had the red carpet rolled out for him in his visits to Saudi Arabia, China, Vietnam, Philippines, etc. Just a handful of liberal UK politician malcontents who don't count!