Under the First Empire, Mexico reached its greatest territorial extent, stretching from northern California to the provinces of Central America (excluding Panama, which was then part of Colombia), which had not initially approved becoming part of the Mexican Empire but joined the Empire shortly after their independence. This region was formally a part of the Viceroyalty of New Spain throughout the colonial period, but as a practical matter had been administered separately. It was not until 1825 that Guatemala created its own flag.