In case it's a fake/invented country, please tell me how will its flag look like, because I'll also add flags in the countries' territory.

Create Amazonia the flag is green with a blue stripe and a white star

CENTRAL AMERICA FOR THE WIN

The flag has a white and red background the white is on the top half and the red is on the bottom half it has a black circle in the middle with the symbol π

Add everything empire. Flag: a crown over earth. Annexed countries: California.

Skullavia black top white circle in middle grey bottom