Short short with English summary                         

トリコロールといえば、青・白・赤の縦縞、フランスの国旗であるが、革命後、1792年に定められた。 その本家はオランダの同色・横縞の国旗で、こちらはそれよりも百年以上まえ、1630年から国旗とされている。 フランスは、当初、そのまま借用して、上下・段々の横縞だった。 イタリアでは、トリコロールといえば、赤・白・緑のイタリア国旗のことだ。 バングラデシュとパラオの国旗が日章旗と良く似た色違いというのは、TVの画面で気の付いた人が多い。 我国の国旗、日の丸は、1500年代頃から、船籍表示に掲げられた。タイのアユタヤ王朝での日本からの傭兵が日の丸を掲げていた絵もある。徳川幕府も明治政府も日の丸を使用した。 英国の保護領とされながらも主権を守ったことで有名なトンガは、カソリックとアングリカンの間でもみくちゃにされたからか、スイスのような十字入りである。 

National flags
The Tricolor is the national flag of France. After the French Revolution, this flag was decided in 1792. The flag was the same flag of Dutch national flag, the Tricolor but horizontally striped. This horizontally striped flag has been the Dutch national flag since 1632 i.e. 160 years older than the French one. And France had for quite long time horizontally striped flag. For Italians, the Tricolor is the Italian national flag, red white green. By the way, the national flags of Bangladesh and Palau are very similar to the Japanese flag. The national flag of Japan, a red sun with white back ground had been used to identify nationality of ships since 1500. There is a picture there the flag is carried by Japanese mercenaries worked for Ayutthaya kingdom in Thailand. There is a nation, Tonga. Tonga is known as a nation which has held her sovereignty even under such long time GB’s protectorate. The national flag of Tonga is somehow similar to Swiss’ perhaps showing how the nation suffered under the period of conflicts between Catholics and Anglicans.
All the national flags of Scandinavian nations use a single cross as the main motif. There is a small group of islands between Sweden and Finland, Aaland. Aaland is a Finish self-governing dominion. Its people speak Swedish, the flag resembles Swedish flag but the national emblem is the Finish one. These Scandinavian nations are not catholic but they emphasize they are Christians. English flag is also a cross and they are not catholic. Actually there are not so many catholic nations with their flags of the cross deigns; only Swiss, Greece and Georgia.
Talking about cross flags, the southern states of US used the diagonal cross designed flag under the American Civil War. This motif, a diagonal cross, is simple and clear. But few national flags have this motif, only Jamaica. North Ireland’s official flag is also a diagonal cross. You can find it in the Union Jack.
I got asked which nation has a single colored flag without any design. I didn’t know. The answer was the flag of Libya (1977-2011), green. We Japanese had single colored flags in the period of 1180-1185. Red flags against white flags. The whites won and the Kamakura period began.
My local patriotism says the Japanese national flag is the best designed: Simple, clear and functional. The easiest flag to identify from many flags at the Olympic Games or from the long line of flags in front of the UN Headquarters is the Japanese flag. Concerning to the motives, the most used mark is a star. So many stars are on the flags of US and EU. And the armed forces, army in the world use star as the international trade mark. Does it prove the nation and the force are same and one?