I'd have prevented the fall of the British Empire and ensured continued hegemony (well, multi-polar hegemony).
1) I would have ceded Austria, part of Poland and part of France to Germany potentially preventing the outbreak of WW2. In return they would leave the remainder of eastern Europe and France and allow us unrestricted access to the Baltic Sea.
2) I would have ceded Canada to the USA (many people don't know it but there was actually a very real threat of war between the USA and UK as late as the 30's). In return they would have ceded Hawaii to the British Empire and agreed to stay neutral in what was to follow.
3) With the Germans and USA out of matters i would cede India to the Japanese in exchange for an alliance.. and the invasion of the USSR from both sides. Gunboat diplomacy would ensure the Swedish don't present a problem in allowing use of their ports.
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Having prevented war with Japan and decimated Russia i would have prevented development of the nuke for a while and the widespread bombing of Britain given British air and naval superiority. As such, the British Empire would largely remain in tact.
I would however have then withdrawn from Eastern Africa with the exception of invading Madagascar and possibly negotiating with Spain and the USA for further Caribbean territory.