Under orders from President James Polk, General Zachary Taylor leads about 1,500 American troops into the disputed Texas-Mexico border area that lay between the Nueces and Rio Grande rivers. Taylor's men begin building Fort Texas (later Fort Brown) on the bank of the Rio Grande, across from the Mexican town of Matamoros. (By Matthew Pinsker)

Mexico begins preparing troops for possible war with the United States. (By Brian Bockelman)