Fire is the element of power. The people of the Fire Nation have desire and will, and the energy and drive to achieve what they want.
Earth is the element of substance. The people of the Earth Kingdom are diverse and strong. They are persistent and enduring.
Air is the element of freedom. The Air Nomads detached themselves from worldly concerns, and they found peace and freedom.
Water is the element of change. The people of the Water Tribes are capable of adapting to many things. They have a sense of community and love that holds them together through anything.