FOREIGN POLICY Magazine write a column, on if Texas actually did try to go independent:

http://blog.foreignpolicy.com/posts/2009/04/16/foreign_relations_with_texas_if_it_secedes

My favorite analysis?

"It would be the world's thirteenth largest economy -- bigger than South Korea, Sweden, and Saudi Arabia. But its worth would crater precipitously, after NAFTA rejected it and the United States slapped it with an embargo that would make Cuba look like a free-trade zone. Indeed, Texas would quick become the next North Korea, relying on foreign aid due to its insistence on relying on itself.

...

...the state of Texas would rapidly become direly impoverished, would need to be heavily armed, and would be wracked with existential domestic and foreign policy threats. It would probably make our failed states list in short order. Probably better to pay the damn taxes."