The Mexican American War was fought in  Texas, New Mexico, California and Central, Northern and Eastern Mexico including Mexico City. It ended in 1848 with the Treaty of Guadalupe Hidalgo in which Mexico was forced to sell Alta California and New Mexico to the United States for $15 million.

What were the Causes of the Mexican American War?
What were the Causes of the Mexican American War? The causes of the Mexican American War were:

• The goal of James Polk for American territorial expansion

• The ideals of the Manifest Destiny

• Cultural differences between the Mexicans and the Americans settlers in the area

• The refusal of Mexico to acknowledge the independence of Texas and its admission to the United States

• Border disputes - Mexico claimed the Nueces River as its northeastern border, while the U.S. claimed the Rio Grande River

Mexican American War: Manifest Destiny
Mexico never acknowledged the independence of Texas and protested against its admission to the United States and disputed the border. Offers were made by the US to purchase the land but Mexico refused.  President James K. Polk, with his belief in the Manifest Destiny of the United States (the conviction that Americans were divinely ordained to expand and dominate the continent) ordered General Zachary Taylor to march to the Rio Grande and occupy the disputed territory. Taylor was attacked by  the Mexicans and the United States declared war on Mexico

The Mexican American War Summary for kids
The summary of the Mexican American War can be divided into three parts:

• The seizure of California led by Stephen Kearny (detailed info can be found in the article on the Bear Flag Revolt and the California Republic)

• The Mexican campaign headed by General Zachary Taylor across the Rio Grande

• The Mexican campaign headed by General Winfield Scott that ended in the capture of the City of Mexico

The Mexican American War Summary: The General Zachary Taylor Campaign
The Mexican campaign led by General Zachary Taylor in the Mexican American War started with his orders from President James Polk The objective of the Taylor's campaign was to  preserve the line of the Rio Grande and then to advance into Mexico. The May 8, 1846 Battle of Palo Alto, the Siege of Fort Texas and the May 8, 1846 Battle of Resaca de la Palma were fought before the actual declaration of war on May 13, 1846 and resulted in victories for the United States. These victories achieved Taylor's first goal of maintaining the line of the Rio Grande. General Taylor crossed the Rio Grande in September 1846 and outnumbered by the Mexican army, faced a series of defeats. The General Taylor took his revenge at the Battle of Buena Vista on February 22-23, 1847. His victory at the Battle of Buena Vista was the last combat during Zachary Taylor's campaign.

The Mexican American War Summary: The General Winfield Scott Campaign
The goal of the Mexican campaign led by General Winfield Scott in the Mexican American War was that he should land at Vera Cruz, march 200 miles to the city of Mexico and capture Mexico city and force the Mexicans to make peace. Between August-September 1846 U.S. volunteers assemble under General John E. Wool and join General Zachary Taylor and his troops. General Winfield Scott, although still considerably outnumbered,  captured Veracruz with the help of the US navy in the Siege of Veracruz from March 9-29, 1847. Other victories followed en route to the City of Mexico. On August 20, 1847, the troops of General Scott beat the Mexicans in three pitched battles, and on September 14, 1847 he entered the city with his army. The Mexican American War continued with a few minor battles but the Mexican American War had been won by the United States and their victory sealed in the Treaty of Guadalupe Hidalgo on March 10, 1848.

Mexican American War Timeline and Facts for kids
The Mexican American War Facts and Timeline for kids is detailed below. The history of the Mexican American War is told in a factual timeline sequence consisting of a series of short facts providing a simple method of relating the famous people and events surrounding the Mexican American War. 

1821: The Mexicans won their independence from Spain and founded the Mexican Republic. Immigrants from the US settled in Texas and Alta California

March 9-29, 1847: American victory at the Siege of Veracruz

April 17-18, 1847: The U.S. wins the Battle of Cerro Gordo under the leadership of General Winfield Scott

July 1847: U.S. diplomat Nicholas Trist is unsuccessful at reaching an agreement with Santa Anna and the war continues

August-September 1846: U.S. volunteers assemble under General John E. Wool and join General Taylor and his troops.

March 10, 1848: The Treaty of Guadalupe Hidalgo, is ratified by the U.S. Senate on March 10th

May 25th, 1848: The Treaty of Guadalupe Hidalgo  is ratified by the Mexican Congress on May 25th