Why did Mexico lose Texas?

The official Mexican line is that it was because of American aggression.

However, I'd like to postulate that the real reason is that Mexico's leaders at that time did not trust their own people.  ( and still don't )

As Santa Anna marched through Texas in 1836, it appeared all too inevitable that the Texan Revolution was doomed.  But there's one detail that may have made the difference.  What was that?  Readiness.  The Mexicans weren't ready for the attack.  They were denied their weapons because their commanders didn't trust them with their rifles.  In a quick moving scenario, such as the attack at San Jacinto, there simply wasn't enough time to get rifles to all the men.  They were overwhelmed quickly.  Now, if they had their weapons on them at all times, this wouldn't have been possible.  Their lines would have held and the attack would have been stalemated, most likely.  This would have been tantamount to defeat for the Texans, who desperately needed a victory.

A well-heeled and arrogant ruling class does not trust its people.  It is weak and can be defeated easily by a much more determined yet smaller attacking force.

This is why you need a 2nd Amendment.  A country of free men is much stronger than a country of mice.