North America 1846: Outbreak of the Mexican–American War

With the annexation of Texas, the US inherited that state's boundary dispute with Mexico. In a bid to settle the issue, as well as purchase the Mexican territories of Alta California and New Mexico, President Polk offered to pay $25 million and forgive damages caused to US citizens in Mexico since independence. The Mexican government refused, prompting Polk to order troops to occupy the disputed land north of the Rio Grande. When Mexico responded by attacking this Army of Occupation, the US declared war.

Main Events

14 Dec 1845–3 Jan 1846 Coup of Mariano Paredes

General Mariano Paredes was in San Luis Potosi, Mexican Republic, with instructions to ready his forces for the coming war with the United States. Instead he alleged a lack of supplies and rose in revolt against President Jose Joaquin de Herrera, marching on Mexico City with his army. Herrera was abandoned by his troops on the 30th, with Paredes entering the capital uncontested on 2 January 1846 to be proclaimed president the following wikipedia

1 Jan 1846 Second separation of Yucatán

The Republic of Yucatán declared its independence from Mexico after the Mexican Congress revoked its wikipedia

8–28 Mar 1846 Crossing the Nueces Strip

The 3,500 troops of the United States Army of Occupation under General Zachary Taylor left Corpus Christi, Texas, to cross the disputed Nueces Strip. On the 28th, they arrived at the Rio Grande opposite the Mexican city of Matamoros and erected the camp of Fort wikipedia

25 Apr 1846 Thornton Affair

1600 Mexican cavalry led by Anastasio Torrejon ambushed 80 United States cavalry under Captain Seth Thornton upriver from Fort Texas along the Rio Grande in the disputed Nueces Strip, killing 11 men and capturing Thornton and 48 others. When he heard of the incident, US President James K. Polk immediately asked for a Declaration of wikipedia

3–9 May 1846 Siege of Fort Texas

1600 Mexican troops led by General Pedro de Ampudia bombarded and surrounded Fort Texas, defended by 500 United States troops under Major Jacob Brown. The fort was relieved after US victories at Palo Alto and Resaca de la Palma, but not before Brown was wikipedia

13 May 1846 US Declaration of War on Mexico

After receiving word of the routing of American soldiers by Mexican cavalry in the Thornton Affair and upon the request of United States President James K. Polk, Congress declared war on wikipedia