The second half of the nineteenth century was a golden age of international law. A new technique developed to stabilize great power rivalry was the regulation of international waterways through treaties. After its opening in 1869 the Suez Canal became a major new trade route between Asia and Europe, and by 1888 it was officially declared a neutral waterway in war and peace alike for all major powers.
The campaign to govern waterways by treaty ran up against imperialist designs, especially in the Western Hemisphere: when the Panama Canal was opened in 1914, it was accessible to international shipping but remained under the direct management of the United States government, which had acquired the land on either side as its sovereign territory, the Panama Canal Zone. Nonetheless, international treaties for maritime bottlenecks persisted in the interwar years. When the Ottoman Empire collapsed in 1922, the League of Nations took over management of the Turkish Straits, but this arrangement was temporary, as Turkey rapidly reasserted its sovereignty under Mustafa Kemal Ataturk. In 1936 an international convention restored Turkish sovereignty over the straits in exchange for their free and uninterrupted use by civilian and military vessels from all nations, subject to certain numerical and weight restrictions. This agreement has held up for ninety years and counting, a respectable duration compared to the shorter shelf life of some other elements of the rules-based international order.
Even in this era of relatively open seas, however, liberal maritime powers did not shy away from the use of coercion. In the nineteenth century Victorian Britain pioneered the protection of global sea lanes as a justification for its preeminence, even though the Royal Navy often restricted trade in the course of wars and diplomatic disputes. It also engaged in gunboat diplomacy against weaker states such as Greece and Argentina by imposing blockades without declaring war—so-called “pacific blockades.” As the saying went, when Britannia ruled the waves, it waived the rules.
The emergence of the United States as a global hegemon after World War II disrupted this state of affairs. The US has espoused the doctrine of freedom of navigation for most of its history, and since the 1940s the US Navy has backed up this commitment everywhere with unique credibility by conducting occasional “freedom of navigation” operations to check what it considers the excessive maritime claims of other countries. During the cold war, Washington undertook such cruises in the Taiwan Strait to contain Maoist China and, in the 1980s, in the Mediterranean to curb the power of Muammar Gaddafi’s Libya. Washington’s Asian and European allies have huddled under the umbrella opened by these displays of American naval power; their assumption has been that US administrations are prepared and able to protect the shipping routes vital to sustaining their economies and societies.