As a result of the development of agriculture in the south, many important cultural advances were made there. For example, the Maya civilization developed a writing system, built huge pyramids and temples, had a complex calendar, and developed the concept of zero around 400 CE, a few hundred years after the Mesopotamians. The Mayan culture was still present in southern Mexico and Guatemala when the Spanish explorers arrived, but political dominance in the area had shifted to the Aztec Empire whose capital city Tenochtitlan was located further north in the Valley of Mexico. The Aztecs were conquered in 1521 by Hernán Cortés.
Upon the arrival of the Europeans in the "New World", the Native American population declined substantially, primarily due to the introduction of European diseases to which the Native Americans lacked immunity. Native peoples found their culture changed drastically. As such, their affiliation with political and cultural groups changed as well, several linguistic groups went extinct, and others changed quite quickly. The names and cultures that Europeans recorded for the natives were not necessarily the same as the ones they had used a few generations before, or the ones in use today.
In the late 18th century and beginning of the 19th, several independence movements started across North America. The 13 British colonies on the North Atlantic coast declared independence in 1776, becoming the United States of America. New Spain, a territory that stretched from modern-day southern U.S. to Central America, declared independence in 1810 becoming the First Mexican Empire. In 1823 the former Captaincy General of Guatemala, then part of the Mexican Empire, became the first independent state in Central America, officially changing its name to the United Provinces of Central America. For more information visit Wikipedia.