In 1836 fifty-nine delegates from various parts of Texas arrived at Washington-on-the-Brazos in the midst of Texas's war with Mexico to hammer out exactly why they were engaged in a war against Mexico. Discontent against Mexican rule had been so extensive that going to war was the easy part. There was broad agreement about the occasions for the war, but it had quickly become clear that there was widespread disagreement about the objective of the war. In particular, there was a considerable rift between those who held that the war should aim at independence and those who held that the war should aim at restoring the constitutional status of the free states of Mexico that had been granted by the 1824 Federal Constitution of the United Mexican States but had been increasingly ignored and then finally repealed in 1835. (The latter was very closely tied to the original reasons for the war, and was a big, big issue. Texas was not the only Mexican state to rebel over it. Yucatan would declare its independence for exactly the same reason a few years later, and a number of other Mexican states began actively refusing to cooperate in various ways with the federal government of Mexico.)
One of the results, modeled on the U.S. Declaration of Independence, was the Texas Declaration of Independence. It bears some remarks of the inconsistencies in the Texas position (e.g., it lists as causes of war both the repeal of the 1824 Constitution, which established the Catholic Church as the national religion, and the establishment of a national religion), but obviously it came down firmly on the independence side of the debate. That document was signed on March 2, 1836, making this Texas Independence Day.
The Convention also enacted a conscription law and established a provisional government with David Burnet as Interim President and Lorenzo de Zavala as Interim Vice President. (Burnet was not a delegate to the Convention, but had arrived at that time in Washington-on-the-Brazos in the hope of gathering volunteers to assist in the desperate situation at the Alamo. Zavala was a delegate, and had been one of Mexico's most talented statesman.) They also expanded Sam Houston's military authority.
Because of the Mexican Army, Burnet transferred the state capital from Washington-on-the-Brazos to Harrisburg almost immediately. As Santa Anna closed in on Harrisburg, the seat of government was transferred to Galveston on April 13. On April 21, Santa Anna was captured by Houston at the Battle of San Jacinto, which ended the war.