Haikou is the capital and most populous city of the Chinese province of Hainan. Haikou was originally a port city, serving as the port for Qiongshan. Haikou was developed as a port during the Sino-Japanese War following Japanese occupation; after the war, Haikou and Hainan remained under Nationalist control until Landing Operation on Hainan Island, when it fell to Communist rule. Today, more than half of the island's total trade still goes through its ports.