Texas was once a part of Mexico. I'm sure there are history books that tell this story differently, many of which are likely written in Spanish, but:

At the time, the United States was looking to expand, pretty much to our current borders. We had some destiny to manifest. We bought the Louisiana territory from France, murdered just...so many natives for the Great Plains, and we approached Mexico to buy the West Coast. Mexico said no. Texas was a Mexican...state? Territory? Part of Mexico at the time, and wanted to secede from Mexico and join the Union. Mexico didn't like this, the USA did, Texas seceded, temporarily self-governing as a nation as they drew up a constitution and applied for statehood. And Mexico declared war.

The United States won this war. Outright. We conquered the capital, the Stars and Stripes flew over Mexico City. The result was the Treaty of Guadalupe Hidalgo, in which the territory which are now the states of California, Arizona, New Mexico, Utah, Nevada and some of Colorado and Wyoming were ceded to the United States in exchange for 15 million USD plus "paying all debts owed by the Mexican government to American citizens." Mexico gave up any claims to Texas and set the international border at the centerline of the Rio Grande. You notice how the rest of the border from the corner of Texas out to the Pacific are great circle routes? That's how you know they were drawn by treaty...a bit like the 49th parallel.

Now, me personally? I've got no design on Canadian territory. I don't want to annex Alberta. But, it is my understanding that Alberta has its fair share of MAGA hats, which shouldn't even make sense.

I'm speaking from a direction of "those who don't study history are doomed to repeat it."