Some months ago I came across a high school world history book (Human Achievement, 1967 by M.B. Petrovich and P.D. Curtin). It was a typical history book in that it began with discussions of the Egyptian, Roman and the Greek civilizations and ending up with the state of the globe in the post World War II era. It was filled pictures, drawings and with maps showing the changes in national political power throughout millennia. While each map merits a book to describe the times it represented, one map captured my attention when I first saw it; and it still does. I think about what it might mean or how it might be viewed not in an historical context of a century and a half ago but in the context of today’s domestic politics of the US and of Mexico. 
The map shows that much of the culture if not the territory west of the Louisiana Purchase (that is, west of the Mississippi River) was dominated by Mexico (though, in fact, the territory was inhabited by a wide range of Native American civilizations).
Though all of that land was in some way influenced by Mexican culture or politics, bit by bit it was taken over by war or diplomacy by the United States pursuing as early as the late 1830s its policy of “Manifest Destiny.” All the above is my recollection of American history, inaccuracies notwithstanding.
Today, there is a lot of controversy over the issue of illegal immigrants focused mainly on those immigrants coming from Mexico. The US Government has a Border Patrol spread thin along the 1956-mile (~3200 km) border. Groups of vigilantes have emerged to protect the border against illegal alien crossings. The federal government has built fences/walls to keep people from illegally crossing into the US. The State of Arizona has perhaps taken the biggest step so far, when its legislature passed a state law that seeks to weed out illegal aliens based on how a person looks, dresses, walks, talks or even who that person hangs out with and where.
Police are given extraordinary subjective powers to determine “the illegal aliens among us.” Much of the racial profiling aspects of the law was recently struck down as being unconstitutional, but the federal judges ruling will likely be challenged by the Governor of Arizona. There is a lot of angst as well as racial or ethno-language bias in America these days. During hard economic times, there is a backlash by the dominant culture against minority cultures.
The North America map of 1821 keeps reappearing in my mind. It causes me to wonder if the parts of North America that was lost by Mexico during the 1800s due to war and diplomacy are being regained by Mexico in other ways. In the absence of conquests related to Americans’ Manifest Destiny” policy, might not today’s map of North America been still represented by the map of 1821?
Most Americans likely have not seen that 1821 political map, except for a brief moment in middle or high school. Out of sight; out of mind. In the mid-1990s American Political Scientist Samuel P. Huntington wrote about “the clash of civilizations” in reference to his belief that “that people’s cultural and religious identities will be the primary source of conflict in the post-Cold War world” [from wikipedia]. Today, we are witnessing what I believe is really a clash of cultures, and even civilizations, being played out on the North American continent and no one knows how best to address it.
If one were to ask the same question today, “who will feed China?”, the answer would be quite different. China’s economy has been booming for the past 15 years or so. The government has amassed more than a trillion dollars of US currency as a result of a chronic trade imbalance in its favor and against America. That puts it in a position to purchase food, whenever it needs to. It can buy energy resources, new technologies (such as for in-country water transfer schemes), fertilizers and whatever else it is that might be needed to increase crop yields and overall food production. But, even that might not be enough to feed China. There is a phenomenon that has been quietly taking place under the proverbial radar screen, that is, out of the purview of policy makers in most countries.