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So. A little bit of a challenge but not a stupidly hard one and quite a open ended one;
With a POD post WW1 (Central Powers victorious is too easy and too overdone) make as much of the world have a monarchy as possible.
This doesn't have to be a absolute monarch, a completely toothless figurehead is totally fine. Though bonus points if you do get a absolute monarch in a developed nation!
And dictators that class themselves as monarchs don't count.