As one of the Avatar Four Nation, The Earth Kingdom is a massive continent taking up most of the planet's eastern hemisphere, roughly geographically analogous to Eurasia in our world. The Earth Kingdom is home to an order of men and women who practice earthbending, the mystical art of terrakinesis. Most of the series takes place in the Earth Kingdom.
The Earth Kingdom has long withstood encroachments on their borders in the Fire Nation's century-long imperialist war. Though the Water Tribes aid the Earth Kingdom in the war, the conflict continues to progress poorly. Other than the Avatar the Earth Kingdom was the only real obstacle between the Fire Nation and complete world domination, as the Water Tribes have thus far demonstrated that they can only defend their own lands, the poles. However, by the end of "The Crossroads of Destiny," the Fire Nation princess, Azula, was firmly in control of the Earth Kingdom capital city, Ba Sing Se. By the following summer, it is firmly occupied by Fire Nation forces.
The national emblem of the Earth Kingdom is a square inscribed with a circle, at the center of which is a much smaller square (like a Chinese coin). The insignia symbolizes both the literal and figurative depth of the Earth Kingdom. It represents the immeasurable layers of deep rock and minerals which Earthbenders manipulate to maintain their great cities, as well as the depth of the inhabitants' commitment and strive towards the effort of a peaceful and productive way of life. This emblem can be seen on the helmets of Earth Kingdom troops.
Earth Kingdom currency, coins, are composed from metals such as copper shaped into the fashion of the national emblem. The design is also applied to certain large, stone "coins" which are used as weapons by earthbending soldiers.
Based on Toph's passport seen in "The Serpent's Pass," Earth Kingdom is literally written as 土國(tu guó). Coincidentally, this is also the Chinese transliteration and abbreviation for the country Turkey.
