Office of the Historian (website) : Office of the Historian, U.S. Department of State (Github).
All of the XQuery code and data from the website is available at Github.
You will find such goodies as:
Office of the Historian Subject Taxonomy of the History of U.S. Foreign Relations (XML)
Foreign Relations of the United States
The Foreign Relations of the United States (FRUS) series presents the official documentary historical record of major U.S. foreign policy decisions and significant diplomatic activity. The series is published in print and online editions at the U.S. Department of State Office of the Historian website.
Encoded using TEI with additional tools for quality checking.
Impressive but perhaps not as immediately useful as:
I checked and there is an entry for Texas that will need to be updated depending on who you listen to in Texas.
There are XML, Schematron, XQuery files galore so there is plenty of production and/or practice material, depending upon your interests.