In 1821, capitalizing on the temporary weakening of French central authority caused by the death of the Emperor Napoleon on May 5, Bourbonists in Spain rise in rebellion against the 'usurper,' Napoleon's brother Joseph Bonaparte. Heavy fighting erupts in the capital, which falls to the rebels within days, forcing Bonaparte to flee by ship. As word spreads, rebellion does also, until the entire country is aflame.

Technically, the ruler of France and its empire is now the Emperor's son, who has been crowned Napoleon II.

However, the real power is Prime Minister Metternich - and initially, more concerned with consolidating his hold on authority at home than with foreign affairs, then Prime Minister takes no action, trusting the French troops already stationed in Spain to put down the uprising. This will prove to be one of his rare mistakes, for the force on hand is inadequate; before his death, Napoleon had been gradually shifting troops from what had seemed a pacified Spain to other parts of his far-flung empire, including the Polish border of Metternich's native Austria.