During the age of exploration in the seventeenth century, the Dutch lawyer Hugo Grotius formulated the legal principle that the ocean was free (Mare liberum), which became the basis of the law of the sea. During the eighteenth century, each coastal nation was granted sovereignty over an offshore margin of three nautical miles to provide for better defense against pirates and other intruders. As undersea exploration advanced in the twentieth century, nations became increasingly interested in the potential resources of the oceans. By the 1970s, many were determined to exploit resources such as petroleum on the continental shelf and manganese nodules rich with metals on the deep ocean floor, but uncertainties about the legal status of these resources inhibited investment.

In 1974 the United Nations responded to these concerns and convened a Conference on the Law of...