Erik Prince —ex-Navy SEAL, ex-CIA spy, ex-CEO of private-security firm Blackwater —calls himself an "accidental tourist" whose modest business boomed after 9/11, expanded into Iraq and Afghanistan, and then was "blowtorched by politics." To critics and conspiracy theorists, he is a mercenary war-profiteer. To admirers, he's a patriot who has repeatedly answered America's call with bravery and creativity. Now, sitting in a boardroom above Hong Kong's Victoria Harbour, he explains his newest title, acquired this month: chairman of Frontier Services Group, an Africa-focused security and logistics company with intimate ties to China's largest state-owned conglomerate, Citic Group. Beijing has titanic...