The Red Chinese won't attack us since they have too much of an economic stake in the USA. If they were to invade a few Walmarts and Sam's Clubs might be destroyed in the fighting, and Bejing definately doesn't want that.

Russia has the potential to oppose us, but for the meantime their plate is full. After they "re-absorb" Georgia, Belarus, the Ukraine, Chechyna, Moldavia, and the Baltic republics, Russia might decide that the USA doesn't need Alaska anymore.

The marxist Latin American countries lack the military strength and organizational ability to be any more than a nuisance.

The real invasion is coming from south of the border, though our leadership refuses to acknowledge the threat. Within two generations the American Southwest will be overwhelmed culturally and politically by Hispanic immigrants. The irreversable demographic shifting of power has already begun. If anyone doesn't believe that they need to make a trip to Tucson, Las Cruces, El Paso, Albuquerque, LA, Phoenix, or just about any part of the Lone Star State with the exception of east Texas.

Twenty years ago there was a symposium held which had the theme "What will the USA look like in the year 2050 ". After a week of discussion by academic types (economists, political scientists, demographers, historians, etc....), they came to the conclusion that there WOULDN'T be a United States of America by 2050. In their opinion the USA would fragment into different countries. Most of Texas and all of the territory lost by Mexico in 1846-1852 would be incorporated into a Hispanic nation they labelled "Mex-America". Much of the deep south would become "New Africa". Utah and parts of bordering AZ, CO, and NV would be a purely Mormon nation state. The Northeast and the formerly industrialized Great Lakes region would become socialist/marxist welfare states (gee, hasn't that already happened?). The country formed in the American agricultural heartland would end up as the cultural heir of traditional Americanism, but would be in conflict with it's neighbors over control of food resources. I read about this back in the late 1980s and thought it was off the wall, but now I'm not so sure.