the next 100 years is one of my favorite books eva!
Mexico will indeed become America's biggest threat in the future. It was a large natural resources, technology from the United States, an emerging technological class, and having millions of sympathetic people in the US and on it's porous border makes them potentially Americas greatest threat in the next 200 years.
IF they went to war, obviously America would "win", but given their geographical proximity and number of Mexicans in America, they could make it a long, bloody war.
Now i don't think Mexico will become a super power per say, but they more than any other country has the potential to harm America.
That's why it is key to maintain good relations with them. Keep'em nice like Canada.
video cliffs on the book