The early period of Mexican history involves ancient civilizations of the Olmecs, the Maya and the Aztecs. Early Mexicans first developed agriculture, built villages, then cities. Within Mexico there were four main zones of Classic Maya concentration: one in lowland Chiapas and three on the Yucatán Peninsula. After the Spanish conquest the Aztec empire was totally destroyed. The Spaniards brought a new religion, made the native people the second-class citizens and slaves. In 1523 the monks started arriving to Mexico with the aim to help Spain to extend its control over Mexico.
The independence of the country was declared only in 1821. But the way to the total independence was difficult and full of barriers. The young Mexican nation was invaded by three different countries, lost large parts of its territory to the US and underwent nearly 50 changes of head of state. Mexican revolution was a 10-year period of shifting power between opposition and governmental leaders. The attempts to stabilize the situation fell pitifully flat. From 1920 to 2000, Mexico was ruled by the reformists who emerged victorious from the Revolution. One of the major problems of Mexico in the middle of the 20th century was the growth of population.