What territory did Germany promise to help Mexico regain in the intercepted note to the German ambassador?

The correct answer highlights that the intercepted note, known as the Zimmermann Telegram, indicated Germany's promise to assist Mexico in regaining territories lost during the U.S.-Mexico War, specifically Texas, New Mexico, and Arizona. This communication was pivotal in pushing the United States toward involvement in World War I, as it stirred strong anti-German sentiments and was perceived as a direct threat to U.S. sovereignty.

The historical context shows that these territories were significant to Mexico due to their economic and strategic value, contributing to the urgency felt by the U.S. in response to such ambitions. The other options represent various regions in the United States, but none align with the actual contents of the Zimmermann Telegram, making them irrelevant to the question about Germany's promise to Mexico.