The world would be ruled by the glorious British empire of course.
Tea and Scones for everyone, the Queen as the head of state and then by now most countries/colonies would simply be a part of the commonwealth, not ruled by the evil oppressive monarchs that you yanks went all batshit over. America would be like Canada and 'Straya, you'd still have your guns but you'd also have a nicer place to live :D
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They would still happen but with the US as a colony, it would be won within a year rather than 4 and 6 respectively. All that manpower that was sitting on the sidelines profiteering from the carnage, instead having it deployed at the start of the war - Germany would have been blown the -blam!- out before they even reached paris.