Chicanas/os often reject the concept of borders through the concept of "sin fronteras", the idea of no borders. The 1848 Treaty of Guadalupe Hidalgo transformed the Rio Grande region from a rich cultural center to a rigid border poorly enforced by the United States government. At the end of the Mexican-American War, 80,000 Spanish-Mexican-Indian people were forced into sudden U.S. habitation. Some Chicanas/os identified with the idea of Aztlán as a result, which celebrated a time preceding land division and rejected the "immigrant/foreigner" categorization by Anglo society. Chicana/o activists have called for unionism between both Mexicans and Chicanas/os on both sides of the border.