In Britain, free trade became a central principle practiced by the repeal of the Corn Laws in 1846.   Large-scale agitation was sponsored by the Anti-Corn Law League.  Under the Treaty of Nanking, China opened five treaty ports to world trade in 1843. The first free trade agreement, the Cobden-Chevalier Treaty, was put in place in 1860 between Britain and France, which led to successive agreements between other countries in Europe. Many classical liberals, especially in 19th and early 20th century Britain  and in the United States for much of the 20th century , believed that free trade promoted peace.  Woodrow Wilson included free-trade rhetoric in his "Fourteen Points" speech of 1918:
Question: How many years after China's opening of 5 treaty ports did the British repeal the Corn Laws?
Answer: 3