be it enacted by the senate and house of representatives of the united states of america, in congress assembled, that it shall and may be lawful for the president of the united states to cause so much of any territory belonging to the united states, west of the river mississippi, not included in any state or organized territory, and to which the indian title has been extinguished, as he may judge necessary, to be divided into a suitable number of districts, for the reception of such tribes or nations of indians as may choose to exchange the lands where they now reside, and remove there.