The Republic of Rio Grande

 Diplomatic Relations Severed by Mexico, 1845.

In 1836 settlers in Texas declared themselves independent from Mexico. The United States recognized the Republic of Texas on March 7, 1837. On August 23, 1843, the Mexican foreign minister informed U.S. Envoy Extraordinary and Minister Plenipotentiary to Mexico, Waddy Thompson, that U.S. annexation of Texas would be grounds for war. On March 1, 1845, U.S. President John Tyler signed a congressional joint resolution favoring the annexation of Texas. On March 4, 1845, U.S. President James Knox Polk noted his approval of the “reunion” of the Republic of Texas with the United States in his inaugural address. In response, the Mexican Minister of Foreign Affairs informed U.S. Minister to Mexico, Wilson Shannon, on March 28, 1845, that Mexico was severing diplomatic relations with the United States. In December 1845 Texas was admitted to the union as the twenty-eighth state. In April 1846, Mexican troops attacked what they perceived to be invading U.S. forces that had occupied territory claimed by both Mexico and the United States, and on May 13, the U.S. Congress declared war against Mexico.