William B. Travis, the commander of the Alamo sent forth couriers carrying pleas for help to communities in Texas. On the eighth day of the siege, a band of 32 volunteers from Gonzales arrived, bringing the number of defenders to nearly two hundred. Legend holds that with the possibility of additional help fading, Colonel Travis drew a line on the ground and asked any man willing to stay and fight to step over — all except one did.

As the defenders saw it, the Alamo was the key to the defense of Texas, and they were ready to give their lives rather than surrender their position to General Santa Anna. Among the Alamo's garrison were Jim Bowie, renowned knife fighter, and David Crockett, famed frontiersman and former congressman from Tennessee.

The final assault came before daybreak on the morning of March 6, 1836, as columns of Mexican soldiers emerged from the predawn darkness and headed for the Alamo's walls. Cannon and small arms fire from inside the Alamo beat back several attacks. Regrouping, the Mexicans scaled the walls and rushed into the compound.

Once inside, they turned a captured cannon on the Long Barrack and church, blasting open the barricaded doors. The desperate struggle continued until the defenders were overwhelmed. By sunrise, the battle had ended and Santa Anna entered the Alamo compound to survey the scene of his victory.

While the facts surrounding the siege of the Alamo continue to be debated, there is no doubt about what the battle has come to symbolize. People worldwide continue to remember the Alamo as a heroic struggle against impossible odds — a place where men made the ultimate sacrifice for freedom. For this reason, the Alamo remains hallowed ground and the Shrine of Texas Liberty.

[Source: http://www.thealamo.org/history/the-1836-battle/index.html]

[Source: http://www.learner.org/interactives/historymap/states_texas.html]

Negotiations might have been possible if Polk had tried a different approach. Mexico had refused to recognize either the independence of Texas or its annexation by the United States, and when annexation occurred, broke relations and withdrew its minster from Washington. Polk rightly believed that he had to restore diplomatic relations, so he sent a special temporary envoy to Mexico. The Mexicans expected that envoy, John Slidell, would offer an indemnity to settle the Texas question, after which Mexico would receive him or someone else as permanent minister. Instead Polk made Slidell permanent minister and instructed him to open negotiations for the sale of California, ignoring Texas completely.

This did not suit the Mexicans at all. If they started by making a concession on Slidell’s status they would probably never get any settlement on Texas. Also Polk had backed up Slidell by sending troops to the Rio Grande, which Texans claimed was their proper boundary. The Mexican president, José Herrera, was newly in office and not very powerful. He did not dare receive Slidell for fear of being overthrown, as the opposition press was accusing him of planning to betray the country by selling Texas. Since he could not be received, Slidell left Mexico City for a town a few miles away, and Herrera sent troops to the Rio Grande to confront the Americans. Matters had reached an impasse.

Polk now needed an excuse to declare war, expecting at the most to fight a few skirmishes on the Rio Grande and then start negotiating. The Mexicans gave him the excuse he needed. The general commanding their troops on the Rio Grande sent a force across the river, and it ambushed a detachment of Americans and killed or captured all of them. The American general, Zachary Taylor, reported this action as a Mexican attack and concluded: "I presume this means the beginning of war." Polk and his cabinet prepared a declaration of war. Congress, badly divided between war and peace, had to support American soldiers under attack and voted to send supplies and reinforcements, whereupon Polk’s Democratic supporters convinced them that they might as well declare war altogether.

But Polk still did not expect the Mexicans to put up much of a fight. When his brother in Europe learned of what had happened, he wanted to come home and enlist, but Polk told him not to, as the war would soon be over.

[Source: http://www.pbs.org/kera/usmexicanwar/prelude/jp_jp_and_the_mexican_war.html]

The Ley de Colonización, state legislation governing colonization in Coahuila y Texas, was passed in March of 1825. Mexican citizens wishing to move to Texas had first choice of lands, but Anglo settlers were also able to obtain land grants for both ranching and farming purposes. New immigrants promised to abide by the state and federal constitutions, to worship in the Catholic Church, and to display sound moral principles and good conduct. In return, they received land, a temporary tax abatement, and status as naturalized Mexican citizens.

[Source: http://dallaslibrary2.org/texas/exhibits/spirit_splendor/mexican.htm]

The Treaty of Guadalupe Hidalgo was a peace treaty signed on the 2nd of Feburary, 1848, at the Villa de Guadalupe Hidalgo (presently known as Gustavo A. Madero, D.f).  The signing of this treaty ended the war between the United States and Mexico.  By the treaty’s terms, Mexico ceded 1.36 million square kilometers (525,000 square miles) of its territory to the United States in exchange for $15 million US dollars. America also agreed to take over $3.25 million US dollars in debts Mexico owed to American citizens.

The cession included several states, presently known as the states of Colorado, Arizona, California, Utah, Nevada, Wyoming and New Mexico.

[Source: http://www.umich.edu/~ac213/student_projects06/magsylje/outcome.html

1830:

• On April 6, the Mexican government forbids further American emigration to Texas.

1832:

• June 26, the Battle of Velasco. This battle saw the first casualties in relations between Texas and Mexico.
• The Convention of 1832 was called by Texans to ask for reforms in government policy towards Texas. The reforms were rejected by the Mexican government.

1833:

• The Convention of 1833 was another attempt by Texans at reforms and they also drafted a constitution patterned after those in the United States. These measures were also rejected by the Mexican government.

1834:

• Stephen Austin as a representative of the Convention of 1833 was arrested without specific charges.

1835:

• On October 2, the Battle of Gonzales is waged and the War of Texas Independence begins.
• On October 9, the Battle of Goliad takes place and ends with a victory for Texas.
• On October 28, Texans are victorious at the Battle of Concepcion despite being outnumbered 5:1.
• On December 11, the Seige of Bexar ends with the Texans capturing San Antonio.

1836:

• On March 1, the Convention of 1836 begins meeting to sign a new constitution and form a new government.
• On March 2, the Texas Declaration of Independence is adopted.
• On March 6, the Battle of the Alamo is lost by Texas and becomes a rallying cry for the continued struggle for indepencence.
• On March 27, the Goliad Massacre takes place in which Mexican General Santa Anna orders the execution of 400 surrendered Texans. This also becomes a rallying cry for Texas independence.
• On April 21, Texans under Sam Houston soundly defeat General Santa Anna at the Battle of San Jacinto. This victory secured Texas' Independence.

Under the purchase, the United States paid $10 million for approximately 30,000 square miles that runs south of the Gila River, extends east to El Paso and west to California. The purchase -- which included the town of Tucson, in Arizona -- was a major step in resolving an outstanding Mexican American border issue. Prior to the purchase, the border between Mexico and the United States followed the main fork of the Gila River to its junction with the Colorado River. At the time the United States claimed the south fork and Mexico claimed the north fork as their main boundaries. This was the final boundary adjustment between the United States and Mexico.

[Source: http://www.pbs.org/kpbs/theborder/history/timeline/8.html