President Bush’s “comprehensive strategy” on border security aimed at preventing “people from coming here in the first place,” announced last month, does nothing to address the growing phenomenon of global migration. What’s more, it leaves Mexico to clean up a mess it didn’t make. According to the UN's Global Commission on International Migration, the number of people worldwide living outside their country of birth has doubled in the past 25 years, rising to more than 200 million people--or about one in every 30 people on the planet. Most of these are “irregular migrants,” people who migrate without proper documents or...