This is the flag of the Aztec Empire. It comes from a world where the Aztecs defeated Cortez and his troops. This was partially due to Montezuma II having a bit more sense and not being quite as superstitious. Smallpox still ravaged the Aztecs, but due to the more limited exposed they were able to recover by the time the Spanish sent additional expeditions. It soon become obvious that the empire would need to reform itself if it was going to survive the European colonization of the Americas.
The first reform was the structure of the empire. The provinces became much more centralized in their organization. The emperor still ruled over all, but each province sent a group of delegates to represent the needs of the province in a special council in Tenochtitlan. The priests and priestesses also began to slowly phase-out human sacrifice from the traditional religion of the Aztecs. Trade relations were established with multiple European nations both to gain access to European technology and to play the various powers off of each other.
For the next few centuries the Aztecs would be prosperous and would have good relations with their neighbors. They provided troops to the Federated Provinces of Cabotia during their rebellion against the British Empire. To this day the two nations remain close allies to this day. The Aztecs also maintained good relations with the Incan Empire, which also managed to avoid European conquest. The Aztecs went on to expand their territory to stretch from the American Southwest to the tip of Panama, and even managed to nab a few islands of the Caribbean.
The next major wave of reforms occurred during the 19h century. The Aztecs, much like Japan during the Meiji Restoration, underwent a Westernization process. Though from the Aztecs points of view the term would more accurately be Easternization. Industrialization began to take off, and Western clothing and customs were slowly introduced to improve relations with the great powers of Europe. However, the Aztecs did not completely turn their backs on their traditional culture. Aztec clothing still remains very colorful and incorporates many traditional designs, and nose rings are still somewhat popular for men and women. More traditional clothing is usually reserved for special ceremonies and occasions, such as religious festivals and the emperor's birthday.
The Aztecs also still worship their old gods, and many temples and shrines can be found throughout the empire. On the other hand, secularism is on the rise, and many people only perform the old rituals out of habit and tradition. What was once an empire known for its bloodlust is today known as a thriving center of technology and innovation.
The flag features the colors red and green, which are traditional Aztec colors. The maze pattern is a common feature in Aztec artwork. The red snake is the feathered serpent god Quetzalcoatl, god of the winds and one of the most important gods in the Aztec pantheon.