One of the funniest soundbites to come out of National Teabagging Day was Texas Governor Rick Perry threatening secession if the federal government "continues to thumb their nose at the American people" ie continues to collect taxes. Now, you and I may think that Governor Goodhair is just playing to his party's ever-smaller-and-more-extreme base, but the thing to bear in mind here is that Texas actually has a history of seceding from countries it doesn't want to belong to. Texans seceded from Mexico in 1835 because they were afraid the Mexican government would free their slaves, then seceded from the United States in 1861 because they were afraid that the American government would free their slaves. (As a direct result of the 1861 secession, in 1865 the American government freed their slaves.)
Supposing Texas did secede in the near future? How would that work out?
In the first place, some areas of Texas would resist secession, just as areas of Virginia, North Carolina and Tennessee did in the 1860s. In particular, the state capitol of Austin, a hotbed of liberalism and the home of the SXSW music festival, would likely see a West Virginia-style countersecession, with Austin being admitted into the Union as a separate state and acting as an oasis of democratic values and culture, much as West Berlin was during the Cold War. Heavily hispanic areas of Texas near the Mexican border would be the site of an ongoing insurgency funded by Mexican sympathizers. Expect the Texan government to use chemical weapons to put down antigovernment uprisings, leading to the adoption of UN resolutions condeming the practice.
Internationally, there would be almost no international recognition of Texan independence, which would, ironically, be recognized by a handful of rogue states such as North Korea and Cuba. The Texan government, being dominated by black helicopter-type crazy wingnuts, would of course refuse to apply for membership in the UN.
Economically, Texas is dominated by two industries: oil and military bases. The withdrawal of the American military after secession would cripple the Texan economy, resulting in skyrocketing unemployment and a deflationary spiral that would result in the hoarding of Texas currency (officially the Tex, unofficially the Ronnie for the picture of Ronald Reagan on the One Tex note) forcing most Texans to resort to barter.
As the humanitarian crisis in Texas deepens, there will be increasing calls for President Obama to use military force to intervene. Fortunately, it is now a recognized principle of American foreign policy that military intervention is necessary if a foreign country with large oil reserves is suspected of harboring nuclear ambitions. All that is necessary is for the American government to cite evidence of Texan agents seeking uranium yellowcake in Africa and the case for war is pretty much a done deal.
Once the decision to invade and occupy Texas is made, expect to see much government propaganda emphasizing the tyrannical nature of the Texan government and the suffering of minority groups. The actual invasion will likely be carried out by a combination of American troops and Israeli mercenaries relying on a strategy of bribing the commanders of key Texas Ranger battalions to not fight.
Once the Texan government falls, expect the occupation and reconstruction of Texas to go far more smoothly than that of Iraq, since the Obama administration will be run by competent pragmatists rather than incompetent conservative zealots. Using the postwar Allied occupation of Germany as a model, it shouldn't take more than four years to rebuild civil society in Texas to the point where statewide elections can be held and the state can be readmitted to the Union, though there will no doubt be some voices advocating for the division of Texas into two or more states to make future attempts at secession less likely. If these voices prevail, we may see a United States with as many as 56 states with such interesting names as West Louisiana and Baja Oklahoma.