The Comanches kept their promise for safe passage on the Santa Fe Trail, but remained angry about events in Texas. White settlement was steadily taking more and more of Comancheria, and the Texas Rangers were still attacking them. As the frontier advanced, the American army had built a new line of forts, followed by a third line. At first these had been manned by infantry, and the Comanche simply by-passed them. Within a few years, the infantry was replaced by new light-cavalry regiments. In all, it took three lines of forts and most of the army's pre-Civil War strength to keep the Comanches out of Texas.