Northwest Ordinance - Background Info
Great Britain had never owned any land in the Mississippi valley until France ceded the country following their defeat in the French Indian War when the Peace Treaty of Paris 1763was signed  and Great Britain received all French lands east of the Mississippi River. The American War of Independence began on April 18, 1775. Congress advised all the colonies to form governments and adopt constitutions for themselves. This turned the British colonies into independent states - refer to Colonies to States.

Northwest Ordinance - Transfer of State Claims
During this period of dramatic changes in America and changing colonies into states there were a series of State Land Claims. These claims for state land ownership were resolved but legislation was required to provide for the rapid and orderly expansion of the new nation across the continent. This issue was addressed by Congress in the Northwest Ordinance. By 1784 the states claiming western territory had given their land to Congress. This vast possession of land stretched from the Lakes to the Ohio and from the Mississippi to Pennsylvania.