Mexican-American War Timeline
Timeline Description: The Mexican-American War was fought between the United States and Mexico between 1846 and 1848. The war started with the U.S. annexation of Texas and was the result of disagreement over where the Mexican-American border should be. The United States victory resulted in adding more that 500,000 square miles of Mexican territory.

Date Event
March 1, 1845 The official proposal of statehood for Texas is signed by President John Tyler.

President John Tyler signs the proposal of statehood for Texas, but it does not pass through Congress. He is warned by Mexico that annexing Texas could lead to war, but Tyler is determined to make Texas part of the United States.
June 16, 1845 The U.S. officially annexes Texas.

The Republic of Texas is annexed by the United States. However, Mexico does not recognize the annexation.
March 1846 General Zachary Taylor leads U.S. troops past the Nueces River toward the Rio Grande River.

General Zachary Taylor leads U.S. troops on a march toward the Rio Grande River. U.S. troops will occupy the land below the Nueces River and claim the area east of the Rio Grande for the U.S.
April 25, 1846 The Mexican-American War begins.

Led by General Anastacio Torrejon, 2,000 Mexican troops cross north of the Rio Grande River and ambush U.S. troops at Fort Texas. The Mexican-American war officially begins.
May 8, 1846 The U.S. wins the Battle of Palo Alto.

U.S. troops defeat Mexico at the Battle of Palo Alto, the first official battle of the war. General Taylor declares victory when Mariano Arista's Mexican troops retreat.
May 9, 1846 The U.S. wins the Battle of Resaca de la Palma.

The Battle of Resaca de la Palma begins when Mexican troops attack Fort Texas, which they believe is located in Mexican territory. Mexican troops are forced to retreated and suffer anywhere between 250 and 400 casualties.
May 13, 1846 Congress officially declares war on Mexico.

President James Polk addresses Congress and says them that Mexico has invaded U.S. soil and that blood has been shed. Congress approves the declaration of war, but some Americans are against it and think that Polk is simply trying to take more land for the U.S.
June 1846 The Bear Flag Revolt begins.

Concerned about Mexican rule, a group of California settlers rebels against Mexico and declares that California is an independent republic. Independence is short because the U.S. begins occupying California soon after that.
August 14, 1846 Stephen Kearny leads the U.S. army in the occupation of New Mexico.

General Stephen Kearny takes an army of about 2,500 men into Santa Fe, New Mexico. They are met with no resistance and easily take control of New Mexico.
September 20, 1846 The U.S. wins the Battle of Monterrey (September 20-24).

General Taylor captures the Mexican city of Monterrey. Taylor's troops first occupy the city of Matamoros and Camargo before heading south to Monterrey. It is a hard fought battle that results in a series of losses for both sides, but the U.S. eventually wins.
December 1846 Antonio López de Santa Anna declares himself Mexico's president.

Antonio López de Santa Anna returns to Mexico after being exiled to Cuba. He stages a coup against the government and declares himself to be the new President of Mexico.
February 23, 1847 The U.S. wins the Battle of Buena Vista.

General Taylor and General Santa Anna face off near Buena Vista. General Taylor's troops are largely outnumbered but with the use of heavy artillery they are victorious. The Battle of Buena Vista is likely General Taylor's greatest victory of the war and helps him get elected as president of the United States in 1848.
April 1847 The U.S. wins the Battle of Cerro Gordo.

General Winfield Scott leads the U.S. in the Battle of Cerro Gordo. Although U.S. troops are outnumbered by Mexican troops, they kill or wound nearly 1,000 Mexican soldiers, take another 3,000 as prisoner, and seize most of the Mexican army's supplies.
September 14, 1847 The U.S. wins the Battle of Mexico City.

After a week of fighting, General Scott and his troops wear down a weary Mexican Army and seize Mexico City. The Battle of Mexico City marks the unofficial end of the Mexican-American War.
February 2, 1848 The U.S. and Mexico sign the Treaty of Guadalupe Hidalgo.

The Treaty of Guadalupe Hidalgo officially ends the Mexican-American War. The Rio Grande River is established as the U.S.-Mexican border. Under the treaty, Mexico recognizes the U.S. annexation of Texas and agrees to sell California, as well as all of its territory north of the Rio Grande.