Few Anglos lived in San Antonio after the Texas Revolution of 1835–36 as Tejanos (Texas-Mexicans) continued their rule. Juan Nepomuceno Seguin was born into a prominent Tejano family with close ties with Stephen Austin, leader of the first American settlers in Texas.
Seguin became mayor or alcade of San Antonio at an early age and, during the Texas Revolution or War for Independence, he fought on the Anglo side and helped in "the Runaway Scrape" led by Sam Houston (retreat from Mexican General Santa Ana climaxing in the Battle of San Jacinto).
However, his political situation became increasingly fragile because of the changing balance of power and Anglos’ efforts to take control. When the Mexican General Vasquez captured San Antonio in 1842, he announced that Seguin held loyalties to Mexico, leading Seguin’s enemies to denounce him as a spy. Seguin fled to Mexico.
Those Tejanos who remained in Texas often found their livestock and corn stolen; others had their land taken in disputes. After the Mexican War of 1846–48, Seguin returned north.
The writing and publication of the Personal Memoirs of John N. Seguin was part of his effort to set the story straight and appeal to Americans while also lashing out about the conflicted position of Mexican Texans.
from http://historymatters.gmu.edu/d/6531/ (History Matters: U.S. Survey Course on the Web)