How could European republicanism that spread throughout Europe after the American Revolution up to the 20th century be stopped? Countries that were traditionally republics like Switzerland do not have to be changed to monarchies, but how do we stop France, Russia, Germany, Eastern Europe, Italy, Portugal, Ireland, Iceland, Austria, the Balkans etc from all ditching their monarchies so that by the 21st century it is seen worldwide as a popuar European tradition to have a King/Queen.
One possible POD could be the failure of the American Revolution, or maybe butterflying away communism. I know that after Napoleon was ditched, France still went through a period where they had a king before the Franco-Prussian War and even after that there was a pretender that was offered the French throne but refused because of the French tricolour flag, so my thought is that if you keep France as a monarchy then you're gonna stop many of the other European countries from developing republicanism (whether this is true or not)...