On this day [10April] in 1864 the Archduke from the house of Habsburg-Lorraine, used to the easy life in Vienna, became the Emperor of Mexico as part of the French intervention in Mexican politics.
He was the younger brother of Franz Joseph I, who ruled Austro-Hungary for more than sixty years.
It didn't go well for Max -- he was executed in the summer of 1867 when Benito Juarez assumed the presidency of the new Mexican Republic
https://en.wikipedia.org/wiki/Maximilian_I_of_Mexico
https://en.wikipedia.org/wiki/Second_French_intervention_in_Mexico
Makes for some good reading,
and for some interesting speculation about connections with the rebellion of the southern slaveholders happening just to the north.