Which country has a red circle on a white flag?

Japan, and the design is about as old and as spare as a national flag gets - a red disc for the sun on a white field, called the Hinomaru, circle of the sun. The name of the country in Japanese, Nihon, means origin of the sun, which is a description written from the perspective of China, looking east.

It was not made official until remarkably recently. It had been in use for centuries and was designated the merchant flag in 1870, but no law established it as the national flag until 1999 - and that law was contentious, because the flag and the anthem are associated by many Japanese with the imperial period and the war. Teachers have been disciplined for refusing to stand for it, and cases have gone to the Supreme Court.

The wartime variant with sixteen rays extending from the disc, the Rising Sun flag, is still used by the Japanese navy and is genuinely inflammatory in Korea and China, where it is read roughly as a swastika would be read in Europe. That the plain disc and the rayed version are treated so differently is one of the sharper illustrations of how much a flag's meaning depends on who was standing under it.