Even more amusingly, the United Nations does *not* recognize annexation as an instrument of national policy and might find themselves compelled to step in and assist Texas against the US.
I read your comment as an implication that Texas was annexed by the US. Is that what you meant?
Texas was an independent Republic, as won in the war with Mexico which (by treaty) ceded the lands to Texas that included the current States of Texas, NM, AZ, CA and part of CO. Texas later sold the lands that now are those other States to the US, but the Texas Constitution and agreement to join the USA required that Texas retain property rights to all of its public land.