Communal violence has gripped Burma again, as a Buddhist mob clashed with local Muslims in the town of Meikhtila, killing at least 20 and displacing thousands. The unrest, which forced President Thein Sein to declare a state of emergency on Friday, is a harrowing reminder of the sectarian strife that decimated the country’s western Arakan (Rakhine) state last year, and presents another challenge to the country’s fledgling democracy.