Fusion is the energy of the sun and the stars, and the largest source of energy in the universe. The ITER fusion reactor that has to rise in Cadarache, France, costs billions of euro's to be paid by a number of countries including Japan and the USA. China is already building its own nuclear fusion reactor. It's a battle between lobbyists for power, money and new techniques because all of the great powers want to protect their energy sources. Will the nuclear fusion the energy source of the future? We will know perhaps until 2050. See on Wikipedia a larger definition of Nuclear Fusion and how it works.