Turkey and the United States have agreed in general terms on a plan that envisions American warplanes, Syrian insurgents and Turkish forces working together to sweep Islamic State militants from a 60-mile-long strip of northern Syria along the Turkish border, American and Turkish officials say. The plan would create what officials from both countries are calling an Islamic State-free zone, which the Turks say could also be a “safe zone” for displaced Syrians. While many details have yet to be determined, including how deep the strip would extend into Syria, the plan would significantly intensify American and Turkish military action against Islamic State […]