Here are the correct responses matched to the descriptions:
- Doubled the size of the U.S.; allowed for westward expansion - Louisiana Purchase
- Officially ended the U.S.-Mexican War and established new border between the U.S. and Mexico - Treaty of Guadalupe Hidalgo
- Provided the U.S. with land to expand the Transcontinental Railroad - Gadsden Purchase
- Belief the U.S. should own land from coast to coast; caused by population boom and desire to acquire resources on new land - Manifest Destiny