It would be the "Ku Klux Klan" that is considered to be a domestic terrorist group, since they have a long history of intimidating people (especially blacks and Jews) with whom they disagree and degrade.
The present-day Republican Party is descended from the "Whig Party", and formed mostly out of an opposition to slavery and its expansion. Although it should be noted the present day Republicans barely resemble the original Republicans.
The battle of Concepcion was the first true and major armed conflict of the Texas Revolution/secession from Mexico. It took place on October 28th of 1835 around what became San Antonio Texas. The Rebel Texans were led by James Fannin and the Famed Jim Bowie. The same Jim Bowie that the Bowie knife is named after. The Texans were the victors as they drove the Mexican Army back and sustained minimal losses.The Mexican Army sustained a few dozen killed while the Texans lost only a man