One factor was barbed wire. As farmers and ranchers wisened up, they used the wire to fence in their cattle, destroying the use of cowboys, and taking away one aspect of the "wide open west". Herds of cattle took over the plains and destroyed the grass. In 1883 the big drought struck and water streams dried up and prairie fires grazed. Also the barbed wire and the natural disasters.
Cause it was under Spanish rule
Spain. Spain controlled the slave trade and sold slaves back to the US