The most likely existential security threat to the United States isn't likely to originate from southwest Asian terrorists or a conventional war with China. Instead, it will originate from Mexico's open source insurgency as:
- The Mexican state becomes hollow and unable to maintain any semblance of control over its territory. Fiscal bankruptcy, driven by declining oil revenues and a global economic depression, will eliminate any remaining legitimacy it has with the countryside (already tenuous due to extreme income stratification).
- The narco-insurgency in the northern provinces morphs into a national open source insurgency with thousands of small groups all willing to fight/corrupt/intimidate the government. Many, if not most, of these groups will be able to power themselves forward financially due to massive flows of money from black globalization. The result will be a diaspora north to the US to avoid the violence.
- Economic failure, a loss of legitimacy and economic deprivation in the US creates an environment for the rapid proliferation of domestic groups willing to fight the government in order to advance their economic interests. Catalyzed by connections to Mexico's functional and lucrative bazaar of violence (read "Iraq's Bazaar of Violence" for more on how this works), these groups carve out their own territory in the US. Experience shows that once these groups gain a foothold, they become nearly impossible to defeat (although they can be co-opted).
Sam Dillon, writing for the NYTs, provides us with a good waypoint check on this scenario. Here is a good example of how quickly the infection can spread:
Jerez, a town of 60,000 a few miles northwest of Felipe Angeles in Zacatecas, was until recently a calm place, largely untouched by organized crime, said Abel Márquez Haro, a grocery wholesaler. But recently, scores of men driving Chevrolet Suburbans and carrying automatic rifles established a menacing presence, threatening residents on the street and extorting businesspeople. The identities of the men remain a mystery, but many people in the town say they assume they are traffickers who have abandoned another Mexican state, perhaps to avoid an army crackdown.
The article goes on to explain how these groups are targeting family members of immigrant workers in the US via kidnapping/extortion. The result has been that workers that would have normally returned during an economic downturn, aren't returning due to safety concerns (and many are trying to bring the rest of their families north to safety).
NOTE: IF your are wondering how a global depression might impact national security, this is it (I suspect that the biggest hew and cry will be over how the fiscal crisis has led to the rapid defunding of hideously expensive conventional weapons systems, of no use to this threat). If you want spice, think about the implications of an economic collapse of Pakistan (needs to borrow), Russia (needs $70+ oil), and China (needs growth in US consumer spending).