1000+ years of history changed during one disastrous escape attempt

In 1791 during the French Revolution, Louie XVI and Marie Antoinette attempted to flee Paris one night in order to establish a counter-revolution. Because of their refusal to split up into two lighter, faster, more inconspicuous carriages, Louie XVI was subsequently caught, arrested, charged, and became the only King of France to ever be executed, ending more than 1000 years of continuous French monarchy.