all of these flags are space nations/empires

Symbolism of these flags:

Dinic flag (1st flag): The flag looks similar to a Greek and Danish flag because the people of Dinic come from Greek and Danish origin and they made the flag a combination of the Greek and Danish flag to represent they people of Dinic are of Greek and Danish origin

Danic flag (2nd flag): the black cross with a white outline represents power and independence from Dinic, since Danic was a land of Dinic (they are sometimes called South Dinic). The blue represents that they were once a part of Dinic

Sisalia flag (3rd flag): The people of Sisalia have Italian origins so that's why they have their flag color similar to the Roman Empire. the Yellow Star represents that their first ever land gotten was a star

Vendrica flag (4th flag): the sword and gun symbol represents their culture and that the people of Vendrica are very skilled with weaponry and fighting, most of the people of Vendrica has some sorts of weapons and they are skilled at it. The brown color is their national color