The country with a flag depicting a red circle on a white background is Japan. This simple yet striking design is known as the Nisshoki or Hinomaru and symbolizes the sun. The flag has a long history, dating back to the 7th century, and its design is deeply rooted in Japanese culture and identity. The red circle represents sincerity and brightness, while the white background signifies purity and peace. The flag is a national emblem of pride for the Japanese people.