This educational video shows the historic flags of countries in transition. Some flags correspond to ancient territory or kingdom. These countries are Albania Flag, Germany Flag, South Korea Flag, United Kingdom Flag and Canada Flag.
근데 여기는 잘못 된 정보가 있는데 고려 국기에 그냥 새 1마리만 있는게 아니라 장식득도 옆에, 위에 있는데요. However, there is incorrect information here. Instead of having a single bird on the Goryeo flag, there are decorations on the sides and top as well.