 On 1 March 1845, three days before he left office, President John Tyler signed a bill establishing an offer by the United States to annex the Republic of Texas, which had broken away from Mexico in 1836, and make it a state.This set off an immediate diplomatic crisis between the United States and Mexico over the southern boundary of Texas.Mexico claimed that the traditional southern boundary of Texas was the Nueces River; the U.S. and Texas claimed it was the Rio Grande, further south.