Australia became a commonwealth of the British Empire in 1901. It was able to take advantage of its natural resources to rapidly develop its agricultural and manufacturing industries and to make a major contribution to the British effort in World Wars I and II. Long-term concerns include pollution, particularly depletion of the ozone layer, and management and conservation of coastal areas, especially the Great Barrier Reef. A referendum to change Australia's status, from a commonwealth headed by the British monarch to an independent republic, was defeated in 1999.