from what I have heard it was in part about slavery because of the outside influences of the pro slavery movement that wanted to annex Texas as a slave state.
OK- now I see the problem. You are confusing periods in Texas History. The revolution was not about slavery in the slightest. The Alamo had negligible effects in the strategic sense, however it showed that the Mexicans would not spare families, nor anybody even slightly involved. La Bahia and the Alamo showed that they would not honor any law of war or agreements, and so that coupled with Col. Travis' letter which recieved print space in many Northern and Southern Newspapers so inflamed the US that money poured into the cause- mainly from all places- New York.
Commandancy of the Alamo
Bexar, Feby. 24th, 1836
To the People of Texas & all Americans in the World--
Fellow Citizens and Compatriots--
I am besieged by a thousand or more of the Mexicans under Santa Anna--I have sustained a continual Bombardment & cannonade for 24 hours & have not lost a man--The enemy has demanded a surrender at discretion, otherwise the garrison are to be put to the sword, if the fort is taken--I have answered the demand with a cannon shot, & our flag still waves proudly from the walls--I shall never surrender or retreat. Then, I call on you in the name of Liberty, of patriotism & everything dear to the American character, to come to our aid with all despatch--The enemy is receiving reinforcements daily & will no doubt increase to three or four thousand in four or five days. If this call is neglected, I am determined to sustain myself as long as possible & die like a soldier who never forgets what is due to his own honor & that of his country--Victory or Death.
William Barret Travis Lt. Col. comdt.
The Alamo did buy time, but the whole reason they were there is because they fiddled around too long in destroying the mission and seizing the cannons and powder like they were ordered and got stuck there. Fannin did the same thing at La Bahia and got up to 300 men massacred after an honorable surrender (that incident sickened even the Mexican Officers who heard of it). All the dilly-dallying by the misc units bought time, and Santa Anna rather than going directly for Houston's main force deciding to sweep up each little band of rebels cost him the war.
The Alamo by some is considered an unfortunate act of delaying good orders, and the Goliad Massacre (La Bahia) was the total disregard of wise orders ending up in that mess.
The period of the Republic of Texas changed dramatically what Texas would look like. In my census figures above you can see the vast increase over two years in population. Some Texans wanted to go immediately to the US. Some stuck it out as a Republic. Sam Houston was in the former camp and was a loyal American- even in the War between the States. As Governor in 1860, he was run out of office when he refused to take the oath of allegience to the Confederacy.
Texas later became quite a slaveocracy, and by the latter years of the civil war, they were disgusted by it. Mr. Wolf writes of a headline talking about the war being "A poor man's fight for a rich man's n----r".
You have just been confusing the Texas rebellion with the Texas annexation period.
However- the decision to annex Texas into the United States 10 or so years later had everything to do with slavery. By that time, Texas was well established as a slave state and a young aristocratic Southern culture. Hence you had all the compromises in the Senate about how to do it. There were also problems about the size of Texas and so we were granted the right to do several things and among them we were given the option to split into four states which would have enabled us to gain six more seats in the Senate, but we'd have fought for years over who got the Alamo.