How did the united states acquire native american lands with such ease in the nineteenth century?

The united states acquire native american lands with such ease in the nineteenth century as by Indian Removal Act made he move of tribes voluntary (either become American or let us use your territory. Thank you for posting your here. I hope the answer helps. 

C. it's a true fact. i know because we are studying about the great depression. so it best illustrates a claim of fact. thx. have a wonderful day!

Is there not a question though?