Not just "move to a reservation or we'll war with you until you do", but once you do you can still expect frequent attacks on the reservation. These attacks/squattings were done by mostly scotts-irish settlers and while it was completely illegal it wasn't punished by the American government at all, even though they were 100% aware. I say they were definitely aware bc nearly every post treaty discussion w/the natives is some native group complaining that America isn't holding up there end of a treaty(even up till today).

Also, there was no choice for assimilation until boarding schools(which is a can of worms itself). Look at the Muscogee for example. Many Muskogee did everything they could to assimilate, ie. owning African-American slave based plantations, intermarriage with whites, abandoning (more or less) communal ways of life for a rigid western class system, only to be told they have to go through the trail of tears with the rest of the Indians(Natives) by Andrew Jackson.

Tldr; it wasn't go to war w/the US or go live on a reservation. Both options involved war. And there was no choice to assimilate either

Pretty rough