These countries were all once British colonies. The majority of their first flags were blue British ensigns defaced with a seal. While most of the countries have their own unique design, many still retain some elements of British flags, such as the 1:2 aspect ratio.

Union Jack/Union Flag: Flag of the United Kingdom
The flag of the United Kingdom, commonly known as the Union Jack or Union Flag, is arguably one of the most recognizable flags in the world. […]