The disadvantage that hindered the Mexican army is that they were not prepared for the San Jacinto battle.
The battle of the San Jacinto began when the Texans fires their cannons into the Mexican camp, rushed in and fought the surprised and unprepared Mexicans in hand to hand combat.
The victory of the Texans gives them the independence from Mexico and also opened the door for the continued westward expansion of the United States.
Therefore, in conclusion, the disadvantage that hindered the Mexican army is that they were not prepared for the San Jacinto battle.
