On 22 April 1970 an estimated twenty million Americans took part in teach-ins, marches and clean-ups in the first Earth Day, organised to press environmental concerns onto the political agenda. The event helped consolidate a broad environmental movement spanning pollution, conservation and public health. Within the year the United States established the Environmental Protection Agency and soon passed major clean-air and clean-water laws. Earth Day later became an annual global observance.
It marked the political arrival of mainstream environmentalism, launching the regulatory framework that would constrain how cities pollute, build and consume land.
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