The struggle for Mexican independence took place under a number of flags, but, when it was finally achieved in 1821 under the conservative Iguala Plan, a tricolor of green-white-red was officially established. This design may have been influenced by the French Tricolor, but the colors were distinctively Mexican. Green symbolizes independence, white is for the Roman Catholic religion, and red is for union—the “Three Guarantees” of Iguala. That political compromise allowed Mexico to free itself from Spain while preserving the supremacy of Roman Catholicism and the social system in which the privileged Creoles ruled over those of mixed ethnic backgrounds and the Indian majority. The central emblem on the tricolor shows in graphic form the foundation myth of the ancient Aztec empire.

Source: Britannica