The colonization of New Spain took place as a northward expansion over increasingly harsh geography, in regions that were occupied by tribes angered at the encroachment; they formed loose confederations of indigenous peoples to resist the settlers. Spain financed the expansion by exploiting mineral wealth, enslaving or forcing indigenous peoples to labor in mines. It established encomiendas for raising livestock, thereby displacing the local people. The indigenous peoples of the North-Eastern quadrant of New Spain (Nueva España) proved particularly resistant to colonial pressures. The Chichimec, Apache, and other tribes resisted conversion to Christianity, and avoided being impressed as laborers or slaves on Spanish ranches and in mines. The Spanish believed such peoples made the frontier ("frontera") a lawless region.