"The ultimate cause of the Illinois decline was the colonial expansion of European nations."
The ultimate cause of the Illinois decline was the colonial expansion of European nations. As France sought to establish a fur-trade empire in Canada, British colonies grew along the Atlantic seaboard and Spain established footholds in Florida and Texas. During the late 1700s, Americans began settling the Ohio River valley and Spain took over the area of Louisiana located west of the Mississippi River. The Illinois got caught in a vise that applied pressure to them from all directions. Warfare and disease caused massive depopulation, while the adoption of European beliefs led to the abandonment of traditional ways of life.