 In 1763, at the conclusion of the French and Indian War, the entire area of Louisiana was divided, with Great Britain receiving the lands east of the Mississippi and Spain claiming the lands west of it.The new city of St. Louis, in present-day Missouri, became the seat of government of Spanish Upper Louisiana.The government of the British side, present-day Illinois, remained in the hands of military commandants at Fort de Chartres; upon that fort's abandonment the seat of government moved to Kaskaskia.