Summary:
First season: It is the year A.D. 2307. Fossil fuels on Earth have been depleted entirely, with mankind turning to the next available power source: solar energy. During this time, 3 orbital elevators with solar power generation systems are built, each under control by the Union of Solar Energy and Free Nations (formerly United States of America), the Human Reform League (Russia, China and India) and the Advanced European Union. However, not all countries are able to enjoy the benefits of this system, leading to widespread resentment and war. Arising out of the conflict, a mysterious military organization known as Celestial Being appears, dedicated to end all warfare using Mobile Suits called Gundam. This begins the stories of Gundam Meisters (pilots) Setsuna F. Seiei, Lockon Stratos, Allelujah Haptism and Tiera Erde as they are thrown into conflict between the 3 superpowers and the various other factions.

Second season: 2312 A.D. Four years have passed since the final battle between Celestial Being and the UN Forces. Humanity, after having established the Earth Sphere Federation, forms an independent security force, A-LAWS, separate from the formal Federation army to further unify nations and the will of mankind. But in reality it is simply inhumane oppressing anti-government powers, doctrines, and ideologies in the name of unity. Setsuna F. Seiei, after surviving the battle four years ago, has decided to once again fight with his Gundam.
(source: ANN)