Look at the mexican cession and think about where the united states began back in 1776

During the seventeenth century the United States began to organize its borders between Canada, then the United States was buying their states from settlers like Louisiana. in 1813.

Texas won against the Mexicans at the Battle of San Jacinto and joined the United States in 1848.

Since Mexico had lost the war for the territory between 1846-1948, Mexico ceded these states in the treaty called Guadalupe-Hidalgo where the United States paid for it up to 18 million dollars and the border was limited as of today.

I hope it help you            

i think the answer is c, rivers.

explanation:

sometimes, borders fall along natural boundaries like rivers or mountain ranges. for example, the boundary between france and spain follows the crest of the pyrenees mountains. for part of its length, the boundary between the united states and mexico follows a river called the rio grande. the borders of four countries divide africa’s lake chad: niger, chad, cameroon, and nigeria.