Nukes. If we have nuclear weapons, they're going to be a lot less likely to try sending in troops. Texas, as an independent nation, would have to obtain control of their nuclear arsenal as their first action.

Recognition. Russia's not too happy with the US right now, so we ally with them, first. Putin might be a dictator, but he's based. Mexico, likewise, would benefit from a weakened United States, and would recognize us quickly. Brazil makes three, with Bolsonaro.

Finances. We'd then need to establish a line of credit with another country, which shouldn't be too difficult with Texas' oil reserves. The main issue here is that we don't want to get involved with the World Bank if we can help it. Once we establish financial ties, though, we're on course.

Convention. We use secure processes to elect officials to draft a new Constitution based on the old one, but with stronger language and stronger protections. We write those secure processes right into our founding documents.