Yesterday I said without qualification that Mexico was in North America because it lay on the North American Plate--the plates constituting the hard crust of the earth. Jim, mi esposo, said he wouldn't say that: plate tectonics didn't exist when Mexico was first considered part of North America. And when was that? Hmmmm....Long before plate tectonics were theorized about and studied.
So how did Mexico come to be part of North America? This is a nice, messy topic to research by shuffling through google.
By the way, North America is not just Mexico, Canada and the US. It is also Greenland, Bermuda, Clipperton Island, and Saint Pierre and Miquelon. Huh?
Anyway, Mexico is shall we say geographically part of North America because it is mostly on the North American plate. Apparently some geographers consider the part of Mexico below the Isthmus of Tehuantepec to be in Central America. The Isthmus is the narrowest part of Mexico.
Certainly above the Isthmus, Mexico just looks like part of North America (although many Europeans do, in fact, consider it part of Central America):
(map from The Encyclopedia Britannica)
"People" tend to want to lump Mexico with Central America because Spanish is the dominant language in both, and, except for the giant exception of Brazil, in South America. But as was pointed out here, that's kind of stereotyping. though calling Mexico along with the other countries of Central and South America Latin countries isn't. French, Portuguese and Spanish, spoken in Latin America, are all Latin languages. (So maybe Quebec should be in Latin America as well as those two French islands).
I have another idea about why Mexico is in North America. And started there even before the US did. Here is a map of the part of New Spain which lay in North America at the start of the Mexican Revolution in 1810:
You can see, even excluding Central America, that New Spain on the eve of its becoming Mexico occupied more of North America than did the United States.
The map below makes this even clearer (You have to include Mexico in your mind here):
The US as STATES in 1810 was the orange part. The blue part included territories and the green part was the Louisiana Purchase. (Don't forget to include Mexico -- or New Spain -- south of the current US in your mind.)
Independent Mexico in 1824 was no different:
The first big change (and everything Texas is big) came as the result of the Texas War for Independence from Mexico fought in 1835-1836, resulting in the Republic of Texas. While I'm not going to go into it here, this was no simple thing. *Santa Ana´s defeat of the Texans at the Alamo seems to have been a catalyst leading a sufficient number of men to join the Texans for them to finally defeat the Mexicans at the Battle of San Jacinto. Of the original defenders of the Alamo, 13 1 were native-born Texans [Texians] with, according to Wikipedia, 11 of those being of Mexican descent. One of them at least, Juan Seguín, still has descendants in San Antonio including my former boss at the University of Texas Health Science Center who was quite clear that he wasn´tof Mexican descent (except insofar as the area had become Mexican) but of Spanish descent, one of the people who came from the Canary Islands. You might also like to know that at least until the 1990s -- maybe no longer-- there were Mexican descendants of the owners of what became the King Ranch still in court trying to reclaim their land. Slavery was banned in Mexico, and when Texas gained its independence from Mexico, it legalized slavery.
Mexico and the US disputed the border of the State of Texas with Mexico claiming that it was the Nueces River, the US claiming it was the Rio Grande (Rio Bravo in Mexico).
In the map below you can see that the Nueces River cuts the lower bump from Texas, more or less.
The dark green section (Texas today) is divided from the light green section (Mexico today) by the Rio Grande (Rio Bravo).
As a result of US insistence that the Rio Bravo be the boundary, Mexico broke diplomatic relations with the US. And this pretty much marks the beginning of the First War of United States Intervention in Mexico, or as the US says, the Mexican American War.
The two countries have noticeably different ideas about this war, and it is really worth learnig about them. A short piece in English talking about the Mexican version can be found here. In fact the PBS site covering the US-Mexico war is very good and has quite a number of Mexican and Mexican American authorities as well as a good list of resources. It is really worth looking this stuff up and unlearning some of the history at least I was taught.
The result of the First US Intervention in Mexico (you have to know the US also directly invaded Mexican territory, including Mexico City) is that Mexico lost about 55 percent of its territory and ended up in the shape it is today. This was not only a result of the battles, but of the US rewriting, on its own, the treaty the two countries had agreed on. The map below shows the negotiations over the Mexican border from 1845-1848.
The last little bit, between the red line and the dotted-dashed line to the south, representes the Gadsden purchase of an area called La Mesilla. The US bought it for ten million dollars, threatening Mexico with more war if it wouldn't sell it.
Obviously, the Mexican-US war is another topic on which I could go on forever. For the purposes of the original discussion, however, which was over why Mexico was in North America, as you can see that it only was reduced to its current size in 1848. So it was part of North America in its combined role as Mexico and part of New Spain, established in the 16th century, for longer than the United States was even the British colonies.