http://www.un.org/depts/los/convention_agreements/texts/unclos/closindx.htm
"The oceans had long been subject to the freedom of-the-seas doctrine - a principle put forth in the seventeenth century essentially limiting national rights and jurisdiction over the oceans to a narrow belt of sea surrounding a nation's coastline. The remainder of the seas was proclaimed to be free to all and belonging to none. While this situation prevailed into the twentieth century, by mid-century there was an impetus to extend national claims over offshore resources. There was growing concern over the toll taken on coastal fish stocks by long-distance fishing fleets and over the threat of pollution and wastes from transport ships and oil tankers carrying noxious cargoes that plied sea routes across the globe. The hazard of pollution was ever present, threatening coastal resorts and all forms of ocean life. The navies of the maritime powers were competing to maintain a presence across the globe on the surface waters and even under the sea.
A tangle of claims, spreading pollution, competing demands for lucrative fish stocks in coastal waters and adjacent seas, growing tension between coastal nations' rights to these resources and those of distant-water fishermen, the prospects of a rich harvest of resources on the sea floor, the increased presence of maritime powers and the pressures of long-distance navigation and a seemingly outdated, if not inherently conflicting, freedom-of-the-seas doctrine - all these were threatening to transform the oceans into another arena for conflict and instability.
In 1945, President Harry S Truman, responding in part to pressure from domestic oil interests, unilaterally extended United States jurisdiction over all natural resources on that nation's continental shelf - oil, gas, minerals, etc. This was the first major challenge to the freedom-of-the-seas doctrine. Other nations soon followed suit.
In October 1946, Argentina claimed its shelf and the epicontinental sea above it. Chile and Peru in 1947, and Ecuador in 1950, asserted sovereign rights over a 200-mile zone, hoping thereby to limit the access of distant-water fishing fleets and to control the depletion of fish stocks in their adjacent seas.
Soon after the Second World War, Egypt, Ethiopia, Saudi Arabia, Libya, Venezuela and some Eastern European countries laid claim to a 12-mile territorial sea, thus clearly departing from the traditional three-mile limit.
Later, the archipelagic nation of Indonesia asserted the right to dominion over the water that separated its 13,000 islands. The Philippines did likewise. In 1970, Canada asserted the right to regulate navigation in an area extending for 100 miles from its shores in order to protect Arctic water against pollution.
From oil to tin, diamonds to gravel, metals to fish, the resources of the sea are enormous. The reality of their exploitation grows day by day as technology opens new ways to tap those resources.
In the late 1960s, oil exploration was moving further and further from land, deeper and deeper into the bedrock of continental margins. From a modest beginning in 1947 in the Gulf of Mexico, offshore oil production, still less than a million tons in 1954, had grown to close to 400 million tons. Oil drilling equipment was already going as far as 4,000 metres below the ocean surface.
The oceans were being exploited as never before. Activities unknown barely two decades earlier were in full swing around the world. Tin had been mined in the shallow waters off Thailand and Indonesia. South Africa was about to tap the Namibian coast for diamonds. Potato-shaped nodules, found almost a century earlier and lying on the seabed some five kilometres below, were attracting increased interest because of their metal content.
And then there was fishing. Large fishing vessels were roaming the oceans far from their native shores, capable of staying away from port for months at a time. Fish stocks began to show signs of depletion as fleet after fleet swept distant coastlines. Nations were flooding the richest fishing waters with their fishing fleets virtually unrestrained: coastal States setting limits and fishing States contesting them. The so-called "Cod War" between Iceland and the United Kingdom had brought about the spectacle of British Navy ships dispatched to rescue a fishing vessel seized by Iceland for violating its fishing rules.
Offshore oil was the centre of attraction in the North Sea. Britain, Denmark and Germany were in conflict as to how to carve up the continental shelf, with its rich oil resources.
It was late 1967 and the tranquillity of the sea was slowly being disrupted by technological breakthroughs, accelerating and multiplying uses, and a super-Power rivalry that stood poised to enter man's last preserve - the seabed.
It was a time that held both dangers and promises, risks and hopes. The dangers were numerous: nuclear submarines charting deep waters never before explored; designs for antiballistic missile systems to be placed on the seabed; supertankers ferrying oil from the Middle East to European and other ports, passing through congested straits and leaving behind a trail of oil spills; and rising tensions between nations over conflicting claims to ocean space and resources.
The oceans were generating a multitude of claims, counterclaims and sovereignty disputes.
The hope was for a more stable order, promoting greater use and better management of ocean resources and generating harmony and goodwill among States that would no longer have to eye each other suspiciously over conflicting claims."
Fuente: http://www.un.org/depts/los/convention_agreements/convention_historical_perspective.htm