18th century is when it began
Hernando de Soto was a Spanish explorer who led the first European expedition deep into the territory of today's United States. Historians worked a lot to trace the route of his expedition. It started in 1539. in Florida: de Soto landed his ships in Tampa Bay. In 1540., they continued to move north-east, through today's Georgia, having heard the gold being mined "towards the sun's rising". The expedition continued trough present-day South Carolina and then to north, across Appalachian Mounthains of North Carolina, and after that entered Tennessee. In 1941. de Soto and his expedition turned westwards, and reached river Mississippi. De Soto was the first European man that crossed Mississippi. They continued trough modern-day Arkansas, Oklahoma and Texas, and later returned to Mississippi. De Soto died in 1942.
It promoted the (relatively) rapid diffusion of immigrants, language, and domesticated crops and animals. Those factors are examined in excellent detail in Jared Diamond's book, "Germ, Guns and Steel" which I highly recommend for anyone studying the development of world cultures. It's a long read, but well worth it.
A).competition over land - they both wanted the Ohio River Valley
