The One Place Where the U.S. Needs to Back Off and Let China Do Its Thing

Iran and Saudi Arabia have resumed diplomatic relations after a seven-year suspension, thanks to mediation by China. Some experts fear this bodes an acceleration of the decline of U.S. influence in the Middle East, in China’s ascension as a global power, and in Israel’s isolation. But in fact, Beijing’s move is, for the most part, a good thing.

There are at least four reasons.

First, the tension between Iran and Saudi Arabia, which has sparked proxy wars, terrorist attacks, and other provocations, is the biggest source of possible war in the region. Calming that tension is in...