Newly assembled data show that, as China opened up to global trade during the early 20th century, its exports became more unskilled-intensive and its imports more skill-intensive. Difference-in-differences estimates show that World War I dramatically increased Chinese exports, raising the relative demand for the unskilled workers producing them. When the war ended, trade costs declined and China's terms of trade increased, further stimulating exports. A simulation of a dynamic general equilibrium model demonstrates that the effects of the war on China's terms of trade produces a decline in the skill premium similar to what China experienced in the 1920s.