It was bold that Trump gave a shout out to Manifest Destiny. I believe the line he used was "Americans tamed the wild west" or something to that effect. In reality why wouldn't Americans of the time believe in Manifest Destiny? What is the alternative. Let these primitive people who never advanced past a hunter gatherer lifestyle control vast sections of the country? Would the Sioux still be out hunting deer and spearing fish today? Would they still be in continuous battle with other Indian tribes? It wasn't a realistic path forward for them.