Answer:
Correct answer is Gadsden Purchase.
Step-by-step explanation:
Gadsden Purchase is the correct answer as according to it United States in 1854 gained a territory that later became a part of Arizona and New Mexico.
Louisiana Purchase is not correct as this is actually the first step towards the westward expansion.
Mexican Cession was a term used after the treaty of 1848 when US gained territories in the south.
Annexation of Texas happened in 1845, and according to it Texas became a part of US.