Relations between the two countries, long bound by common interests in oil and security, have strained over what some analysts see as a more assertive Saudi foreign policy.

Tens of millions of Chinese now identify as Christians, and the number has grown rapidly, posing challenges for a government that is officially atheist and wary of threats to its power.

U.S. missile defense in the twenty-first century is focused on emerging threats from North Korea and Iran, but critics say these systems are too costly and largely unproven.