I live about half way between downtown San Diego and downtown Tijuana. I'm going to construe this geographic proximity to mean that I'm qualified to share the following tidbits that readers in places like Australia might have missed.
Remember the Alamo!
The Mexican Army wasn't attacking those Americans because they were unwelcome in Texas. Americans were welcome to settle in Texas, they just weren't allowed to hold slaves, something that Mexican law prohibited. Why did the Mexican Army attack Davey Crockett, Jim Bowie and friends at the Alamo? Because they were slaveholders who refused to obey Mexican law.
California for Americans!
At one point, Russia, Mexico, and the United States all had claims on California but none of them had a presence that allowed them to enforce those claims. Settlers from various parts of the world lived together across this big sprawl of a state. After gold was discovered in 1849, a motley, self-appointed army "invaded" Monterey and claimed it as part of the U.S. They were neither officially sanctioned nor prohibited by the U.S. government. This little army then headed south to Los Angeles to add it to their conquests. When the residents there heard that Monterey's property prices rose by 50% once it was declared to be a part of the U.S., they promptly surrendered to this "American" army. Ever since, home prices have fueled millions of dinner conversations and motivated many a Californian policy proposal.
Turmoil in Mexico!
Progress is boring. Emotional upheaval may be dramatic, but it interferes with the stability needed for people to focus on inventions, novel writing, or creating a business. In 1700, per capita GDP in the U.S. and Mexico were roughly the same ($490 and $450). By 1800, the U.S. per capita GDP was not quite double ($807 vs. $450), but by last year, the U.S. per capita GDP was about four times Mexico's ($43,500 vs. $10,600). Why did Mexico fall behind? It may have to do with political turmoil. Between 1824 and 1867, the U.S. had 13 presidential administrations; Mexico had 52, or 4 times as many. Could it be that 4 times as much political turmoil led to one-fourth the per capita income? It certainly sounds plausible to me.