I think a circle could represent so many things.
It could represent the food chain which starts from a plant and comes back to a plant again.
The word "Circle" is used for clubs too, which has the meaning of WA(輪).
A circle is also the opposite of figures with edges such as triangles and rectangles.
I think this could show an endless peace.
In Japanese there is a word "角が立つ" which means to become offensive to someone, and also a word "角が取れて丸くなる" which means to become affable by becoming less offensive.
Both phrases include "角", which never shows up in a circle.
A circle is a round, harmless figure.
