I don’t think invasion is the first step after the dissolution of the US. I think Texas becomes the new center of a southern entity for the reasons mentioned, but the other southern territories becomes vassal states to Texas. Many of the southern states rely heavily on federal aid to exist. Texas will leverage this to use Georgia, Tennessee, Louisiana, maybe South Carolina (plus those you mention) as near slave labor to feed its wealth and influence. As a new constitution is negotiated Texas will emerge as the center of a christofascist nation. Florida maintains a tenuous parity with Texas until rising seas make it uninhabitable. They then plead with the great Texas union to provide aid at which point they become subjugated the same as the others.
On thing is for sure, they’d fix immigration overnight. No one would be trying to escape TO The Holy Christian Union of Texas.
Come to think of it, the first post US armed conflict will likely be the HCUT pushing into Mexico as it grabs for the Panama canal and eventually the natural resources of South America.
I wish I was more creative. I’d love to write a post-American fictional novel.
DAE died a violent death on reddit years ago. I was there. I remember the backlash.
Let’s not revive it here. This place is special.