Final answer:
The event that marked the Texan victory against Mexican forces and secured Texas' independence during the Texas Revolution was the Battle of San Jacinto.
Step-by-step explanation:
During the Texas Revolution (1835-1836), the event that marked the Texan victory against Mexican forces and secured Texas' independence was the Battle of San Jacinto. This decisive battle took place on April 21, 1836, when the Texas forces under General Sam Houston launched a surprise attack on Santa Anna's Mexican troops, who were encamped along the banks of the San Jacinto River.
The battle was swift and catastrophic for the Mexican forces, with approximately half of the Mexican troops killed and the rest, including General Santa Anna, taken prisoner. The victory at the Battle of San Jacinto was crucial, as it led to the signing of the Treaties of Velasco, where Santa Anna agreed to the independence of the Lone Star Republic.