The United States Congress declared war on Mexico on May 13, 1846 after only having a few hours to debate. Although President José Mariano Paredes's issuance of a manifesto on May 23 is sometimes considered the declaration of war, Mexico officially declared war by Congress on July 7. After the American invasion of New Mexico, Chihuahua sent 12,000 men led by Colonel Vidal to the border to stop the American military advance into the state. The Mexican forces being impatient to confront the American forces passed beyond El Paso del Norte about 20 miles (32 km) north along the Rio Grande. The first battle that Chihuahua fought was the battle of El Bracito; the Mexican forces consisting of 500 cavalry and 70 infantry confronted a force of 1,100–1,200 Americans on December 25, 1846. The battle ended badly by the Mexican forces that were then forced to retreat back into the state of Chihuahua. By December 27, 1846, the American forces occupied El Paso Del Norte. General Doniphan maintained camp in El Paso Del Norte awaiting supplies and artillery which he received in February 1847.

Who declared war on Mexico in 1846?