In 1673, Frenchmen Louis Joliet and Father Jacques Marquette explored the areas of the Mississippi and Illinois Rivers, and their voyages led to French claims on the region until 1763, when France ceded the land to Great Britain by the Treaty of Paris. During the Revolution, George Rogers Clark and his army won the Illinois Territory for the Commonwealth of Virginia. In 1784, it became part of the Northwest Territory, and on December 3, 1818, Illinois entered the Union as the twenty-first state. U.S. Route 54 enters Illinois east of Louisiana, Missouri, and stretches northeast toward Pittsfield. In Illinois, the route was dedicated as the 33rd Division Memorial Highway on Memorial Day 1963, honoring the World War I division organized in 1917 from Illinois National Guard units, which played an important role in the Meuse-Argonne Offensive and was used in the Pacific in the Philippines during World War II. Route 54 ends its sixteen-mile journey in Illinois four miles west of Pittsfield, where it meets U.S. Route 36. Pittsfield, the county seat of Pike County, was where John Nicolay began his career and met John Hay, beginning a lifelong friendship. Nicolay wrote a ten-volume biography of Lincoln, and Hay collaborated on it before going on to a career as a diplomat, serving as ambassador to Great Britain and Secretary of State from 1898 to 1905. His major accomplishments included the open door policy with China and the Hay-Paunceforte Treaty.