The correct answer is B. The action that started the war between the United States and Mexico was that President James Polk ordered General Zachary Talyor to claim an area of disputed land for the United States.
Explanation:
Texas declared its independence from Mexico in 1836. Mexican General Jose Urrea ordered the killing of about 1,000 Texan rebels in Goliad and Coleto. After suffering several defeats (the best known was the battle of the Alamo), the rebels finally defeated the troops under Santa Anna in the battle of San Jacinto, capturing the president; he signed the Treaty of Velasco in prison, in which he recognized the independence of the new state and the border on the Rio Grande. Mexico ignored the validity of the Treaty, the independence of Texas and the new border boundary (the boundary between the states of Tamaulipas and Texas was the Nueces River). In the following years there were some military incursions by Mexican troops that came to occupy San Antonio, but ended up retreating each time south of the Rio Grande. In 1845 Texas was annexed to the United States as a state, and that event triggered the events that would lead to war. That same year, tensions grew between the two countries over these territories when the United States government offered to pay the Mexican debt to US settlers if Mexico allowed the United States to buy the territories of Alta California and New Mexico, the proposal being rejected by the Mexican government, breaking diplomatic relations between both neighboring countries.
The sending of troops by US President James K. Polk to the disputed territory on the Texas border, between the Rio Grande and the Nueces River, ended up leading to the first confrontation between troops from both countries, which occurred on April 25, 1846 to the north of the Rio Grande, in the place called Rancho de Carricitos, when a 63-man US patrol, under the command of Captain Seth Thornton was ambushed by forces under General Anastasio Torrejon.
This confrontation gave James Polk the reason to request the declaration of war against Mexico, so the United States Congress declared war on Mexico on May 13, 1846, which would allow him to conserve Texas and appropriate the coveted and rich territories of Alta California and New Mexico as war compensation. Finally, the armed confrontation and the invasion of almost the entire Mexican territory would end with the signing of the Treaty of Guadalupe Hidalgo in 1848.
