A paramilitary policeman watches a flag-raising ceremony at Tiananmen Square ahead of the opening session of the National People’s Congress (NPC) in Beijing, China, March 5, 2016.Reuters

As Chinese President Xi Jinping prepares to host the annual G20 summit next month, two major foreign-policy challenges have begun to simmer between the US and China: The deployment of America’s most advanced missile-defense system to South Korea and China’s role in the disputed waters of the South China Sea.

Here’s a brief look at both issues.