The first person of European descent to describe the Assiniboine was an employee of the Hudson's Bay Company named Henry Kelsey in the 1690s. Later explorers and traders Jean Baptiste de La Vérendrye and his sons (1730s), Anthony Henday (1754–55), and Alexander Henry the younger (1800s) confirmed that the Assiniboine held a vast territory across the northern plains, including into the United States (which achieved independence in 1776 but did not acquire the plains until 1803 in the Louisiana Purchase from France.)