what was the conflict between the native americans and cowboys/settlers?
Native Americans (Indians) had lived and hunted on this land for thousands of years. In the 1600s through the 1800s, their land was invaded by hordes of strange people. These new people settled on the Native's land and took their land away -- often by force backed up by guns. The settlers wanted to farm the Native's land and the cowboys wanted to graze their cattle on the Native's land.
Obviously, this theft of their ancestral lands made the Natives angry and they tried to fight back -- to remove the hated newcomers from their land.