Forty years ago, China adopted reforms that set it on the path to economic rejuvenation and the reclaiming of its position as a regional and global power. This month, China marked that momentous decision with forums and pledges to use its growing strength responsibly. At the same time, however, Chinese President Xi Jinping warned elsewhere about the downsides of interdependence and called for increased self-reliance — a seeming contradiction to the promise to safeguard the global economic order. Which policies will prevail is a matter of grave consequence for the world.

In 1978, Chinese leader Deng Xiaoping made the most important decision in Chinese history. He abandoned the autarkic policies of his predecessor, Mao Zedong, and adopted economic "reform and opening up." Xi toured southern China a few weeks ago, visiting many areas that served as pilot projects for Deng's experiment and promising to continue the policies that he launched.

He repeated that pledge this week at the China Import Expo, a massive event designed to showcase Chinese intentions to be a boost, and not a bane, to the global economy. Speaking to representatives from over 170 countries, Xi said China will purchase $30 trillion in foreign goods over the next 15 years, and another $10 trillion of services in the same period. China would also open restricted sectors such as domestic health care, education, financial services, telecoms and mining to foreign investors. He promised "to lower tariffs, facilitate customs clearance, reduce institutional costs in imports, and step up cross-border e-commerce and other new forms and models of business." More special import zones will be created, existing ones expanded and intellectual property rights protected.