The Mexican-American War began in May, 1846, following a formal Declaration of War by the United States. The issue was the Texas Republic’s request for annexation, further exacerbated by a dispute over international boundaries. Mexico had not officially recognized the Lone Star Republic’s independence from Mexican ownership ten years previously, and now vehemently insisted the boundary was not the Rio Grande but the Rio Nueces father north. President James Polk very much wanted Texas for the Union–and California as well. Leaving nothing to chance, he sent naval warships into California waters. Fighting ended in Mexico City in September 1847, with the United States victorious. The formal treaty to end hostilities was signed February 2, 1848 at Guadalupe Hidalgo, Mexico–granting California, Nevada, Utah, most of New Mexico and Arizona and the disputed Texan regions to American sovereignty for a payment of $15 million dollars in gold and silver. It is doubtful Mexico would have signed the Treaty of Guadalupe Hidalgo had they known of the gold discovery in California just nine days earlier on January 24, 1848.