I've read several of Buchanan's books. He is very well versed in his history, although he can be a bit of an alarmist and a little xenophobic. Those two are the single biggest criticisms against him. He makes great points nonetheless.
The United States is going to go one of two ways in it's future. On the one hand, the North American Union becomes a reality and the currency goes from the fiat dollar to a silver and oil backed Amero. Oil is flowing, the economy has rebounded, and people are generally peaceful with one another. However, a NAU is not a solution to the problems that exist, but only a basic appeasement and pandering to it's citizenry and a delay to the inevitable. This NAU dream is encouraged and has been concocted by globalists and their supporters. It is a direct challenge and partially designed to kill nation soveriegnity and nationalism, two massive roadblocks that directly oppose any kind of globalist agenda, corporate or multi-national.
Now, the other way. I've long held that such differing people cannot live peacefully together without either an economic glue or a brutal dictatorship holding them all together. We see it in Iraq, where Sunnis, Shiites, Kurds, and other groups, foreign and otherwise, are at each other's throats in unconstrained fury. These groups are just fundamentally different from one another and would rather act autonomously from each other. Saddam forcefully held them together via a brutal dictatorship where he held military power. The US military found itself in the middle of all of the infighting, and under basic moralities, human deceny, and sensitivity to world opinion, will absolutely not do what Saddam did to control the populations. In addition, the US would probably have to be even MORE brutal to ensure complete control as we are truly foreigners, instead of being the head of a differing minority group.
Anyway. The US busts along ethnic, cultural, and geographical lines. The diversity and multiculturalism that is taught in our schools and broadcasted over our televisions(dumbboxes) is vastly different than what is practiced in the real world. Only do the majority populations(for now) in the US, Canada, Europe, and Australia swallow this ideal hook, line, and sinker. The idea that "we are all the same" is not embraced by the minority populations in those nations, nor is it embraced in the Middle East or Southeast Asia. Those populations, growing ever more numerous, are quickly being empowered without ever assimilating into the host nation....except assimilating into what they choose, such as the credit markets, Free Speech rights, Assembly, and social programs. In essence, the US will be taken apart, with each differing ethnic and cultural group taking a piece for themselves. When the shit hits the fan, we will not stand together under the Stars and Stripes, but will stand together with those who think, live, and act like ourselves.