The expansion of the continental United States was made complete by A. the Louisiana Purchase
B. the annexation of Texas.
C. the Mexican Cession.
D. the Gadsden Purchase.
HURRY and no spam

I think the Louisiana Purchase

hope this helped

Treaty of Guadalupe Hidalgo

Explanation:

The Treaty of Guadalupe Hidalgo, signed by chief negotiator Nicholas P. Trist on February 2, 1848, and approved by the U.S. Senate on March 10, 1848, ended the war, opened a dramatically different chapter in U.S. relations with Mexico, and nearly completed America's continental empire.

would not cooperate with each other voluntarily.

i thinl it is the 1st answer