I have been enjoying Adam Hochschild’s To End All Wars: A Story of Loyalty and Rebellion, 1914-1918, which covers the British role in World War I. My favorite section details how the British responded when it turned out they had a drastic shortage of binoculars, which at that time were very important for fighting the war. They turned to the world’s leading manufacturer of “precision optics,” namely Germany. The German War Office immediately supplied 8,000 to 10,000 binoculars to Britain, directly intended and designed for military use. Further orders consisted of many thousands more and the Germans told the British to examine the equipment they had been capturing, to figure out which orders they wished to place.
The Germans in turn demanded rubber from the British, which was needed for their war effort. It was delivered to Germany at the Swiss border.
That’s right: the British and the Germans traded war materiel to each other while at war.
I always tell my students that no one is holding a gun to your head to make you trade.
Now, here’s a case of countries with guns pointing at each others’ heads, continuing to trade on a voluntary basis.