[exmachinan]

The Japanese didn't have characters until they got them from China via Buddist texts.

The simplified character for "guo" (koku/goku) was first simplified by the Japanese! After WWII in 1946, the Japanese simplified its characters too, called the Shinjitai. The PRC in the 1950s then copied the Japanese simplification. The reason the Japanese used the "jade" character was that it rhymed in Japanese. Unfortunately it doesn't rhyme in Mandarin, because Mandarin is such a bastardized form of Chinese. In ancient Chinese the two characters would rhyme too.

[maui_hawaii]

How did Japan get Chinese characters at all, meaning in the first place.

[maui_hawaii]

http://www-chaos.umd.edu/history/setting.html

For centuries virtually all the foreigners that Chinese rulers saw came from the less developed societies along their land borders. This circumstance conditioned the Chinese view of the outside world. The Chinese saw their domain as the self-sufficient center of the universe and derived from this image the traditional (and still used) Chinese name for their country--Zhongguo () , literally, Middle Kingdom or Central Nation.