The American frontier, also known as the Old West or the Wild West, includes the geography, history, folklore, and cultural expression of life in the forward wave of American expansion that began with European colonial settlements in the early 17th century and ended with the admission of the last few territories as states in 1912. This era of massive migration and settlement was particularly encouraged by President Thomas Jefferson following the Louisiana Purchase, giving rise to the expansionist attitude known as "Manifest Destiny" and the historians' "Frontier Thesis".