The Seven Years' War preceded WWI by 160 years (1756-63). It was fought between coalition led by France, and one led by Britain. Before the formation of the League of Nations, there was constant reshuffling and alliances to prevent dominance by any one power. The changing Balance of Power resulted in regular wars and traded control of territory. La Florida was the first major land claim by the European Colonisers of the Americas. British victory in 1763 gained them Florida, which was handed back to Spain after the American Revolutionary War. 1783 saw Spain's American colonies at their maximum size. Spain struggled to finance control and eventually ceded it over to the United States in 1821. The area had been a sanctuary for run-away slaves. Britain abolished slavery in 1833, and Spain in 1811. In 1845, Florida was admitted as the 27th state of the US and became a slave state. The Thirteenth Amendment abolished slavery throughout the Union in 1865.