War with Pakistan and Mexico?

The U.S. military has its eye on Pakistan and Mexico as countries considered to be on the brink of collapse. The Joint Operating Environment (JOE) 2008 Report (PDF) states:

Some forms of collapse in Pakistan would carry with it the likelihood of a sustained violent and bloody civil and sectarian war, an even bigger haven for violent extremists, and the question of what would happen to its nuclear weapons. That "perfect storm" of uncertainty alone might require the engagement of U.S. and coalition forces into a situation of immense complexity and danger with no guarantee they could gain control of the weapons and with the real possibility that a nuclear weapon might be used.

The Mexican possibility may seem less likely, but the government, its politicians, police and judicial infrastructure are all under sustained assault and press by criminal gangs and drug cartels. How that internal conflict turns out over the next several years will have a major impact on the stability of the Mexican state. Any descent by Mexico into chaos would demand an American response based on the serious implications for homeland security alone.

How is this any different from the U.S. government's justification for war with Iraq?