By THÉRÈSE MARGOLIS     During the 300 years of Spanish rule following Hernán Cortés’ conquest of Tenochtitlán in 1521, the people of Mexico suffered the indignities of imported smallpox epidemics, forced labor and imposed religious conversions. The disenfranchised indigenous Mexica, Maya, Zapotec and Toltec civilizations were stripped of their heritage and land, and what properties were not claimed by the viceroys