Answer:
Mexico-Tenochtitlan was the capital of the ancient Aztec empire, founded on March 13, 1325. When Hernan Cortes conquered the Aztecs on August 13, 1521, he decided to keep such city as the capital of the New Spain. Finally, when Mexico gained its independence from Spain in 1821, Mexico City was already the cultural, political and economic capital of the country, so the independence revolutionaries decided to keep it as the capital of Mexico.