How Shinzo Abe's exit could threaten regional stability and Japan's alliance with the US

(CNN)Rumors concerning Japanese Prime Minister Shinzo Abe's health had circulated for weeks, and while his resignation on Friday could not have come as a complete shock to United States officials, the timing of the announcement is worrisome. Tensions in Asia have been on the rise. While the US and China trade war marches on, China has been taking increasingly provocative actions in the East China and South China Seas. Just a few days ago, for example, China fired four ballistic missiles into the South China Sea, where six different governments are engaged in a territorial dispute. China has also ratcheted up tensions with Japan by continuing to allow its ships to sail into the disputed...