After the fall of the Aztec Empire, explorers set out to explore the western frontier in the Bajio Region. The Spanish expansion in Nueva Galicia was slowed down by several tribes in the vicinity, such as the semi-nomadic Chichimecas and the Guachichiles. To the east of Pechititan, the Guamares inhabited the Guanajuato area, and to the west, the Zacatecos lived. The Zacateco caudillos (chiefs), Xiconaqui and Custique, along with the Chichimecas, struck down multiple Spanish invasions from 1550 to 1590 in the well-known Chichimeca War.