The debate over maritime jurisdiction is an old one.

The ornate Tower of Belém, with its faded ivory parapets, still stands proudly above the Tagus River, a monument to a distant era. Built in 1502 to commemorate Vasco da Gama’s expedition to the East Indies, the fortress was the final gateway navigators would pass before entering the sea beyond. Further afield, along the shorelines of Africa and Asia, Portuguese explorers erected stone pillars, padrões, as reminders of home and markings for a new imperial domain. In the early 17th century, the parameters of the Estado da India became the subject of an intense international legal contest, the principles of which are still under dispute.

What the Portuguese discovered in Asia was an active free trading zone involving Arab and Chinese merchants converging on cosmopolitan ports such as Malacca. While the West had been disconnected from the East following the fall of Rome, the open waters of Asia represented the height of global commerce. In his classic study An Introduction to the Law of Nations in the East Indies (1967), Charles H. Alexandrowicz reviewed Asian maritime codes and customs. He found that the high seas, from the Arabian Sea to the edge of the Pacific, were freely navigated and considered as being beyond any sovereign’s control.

Following their arrival in 1498, however, the Portuguese established a new order wherein they claimed a monopoly on trade in the East Indies and sovereignty over the high seas. This exclusivity served national security goals (by undermining the economic resources of Islamic enemies, such as the Ottoman Empire, which threatened Western Christendom) and commercial interests (by preventing market access for European competitors). At the end of the 16th century, the Dutch were on the rise and challenging Portugal’s maritime hegemony in Asia.

http://thediplomat.com/2016/05/lords-of-navigation-grotius-freitas-and-the-south-china-sea/