True the war in Europe came to an end on May 8, 1945.
They were treated as slaves. Meaning they were beat, forced to dirty work and even killed.
The reason why cowboys were portayed like a solitary, strapping white men lies on the fact that that cowboy was a late romantic creation. Essentially, the represented the ideal of freedom.
The plantations and farms of Virginia and the Southern colonies were the foundation of the economy of the New World. The colonies grew crops for export. As plantations grew the settlers needed more labor to work them. This was supplied by slaves from Africa.