The expansion of the continental united states was made complete by the louisiana purchase. the annexation of texas. the mexican cession. the gadsden purchase.

The expansion of the continental United States was made complete by the   Gadsden Purchase (1853), today  in the southern states of Arizona and New Mexico. This purchase would define the final frontiers of the  continental territory of the United States.

-an amendment is proposed.

-two-thirds of congress must approve.

-thee-quarters of states must approve.

-the proposed amendment becomes law.

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this is a good question! i'll do some research and come back when i have the answer!