Was there a universal agreement sometime in history that all flags should be rectangles? | AskHistorians Archive Observer

Was there a universal agreement sometime in history that all flags should be rectangles?

by BamParker

j0akime

Past answers:

https://www.reddit.com/r/AskHistorians/comments/1xaadb/why_is_the_rectangular_flag_the_standard_when_did/

Also, some examples of non-rectangular flags through history

https://www.reddit.com/r/vexillology/comments/4fqzpv/non_rectangular_flags/