Occupied by succeeding cultures of indigenous peoples, this area was populated by the historic Osage tribe at the time of European encounter. The region was first settled by Europeans during the rule of the Spanish Empire. The Spanish log fort "San Juan del Misuri" (1796–1803) was built in present-day Washington. After the American Revolutionary War, migrants from the new United States started moving West. Among them were the family and followers of Daniel Boone, an explorer from Kentucky who settled the area starting in 1799. For the next two decades, most settlers came from the Upper South, especially Kentucky and Virginia, bringing their slaves with them to work the land.