Louisiana (New France)
As late as 1783, at the end of the American Revolutionary War, Spain held claim to roughly half of today's continental United States. In the Treaty of Paris France ceded Louisiana (New France) to Spain from 1763 until it was returned in 1800 by the Treaty of San Ildefonso. In 1775, Spanish ships reached Alaska. From 1819 to 1848, the United States and its army increased the nation's area by roughly a third at Spanish and Mexican expense, gaining among others three of today's four most populous states: California, Texas and Florida.