OTTAWA—Canada’s military mission in Afghanistan ended Thursday, hours before suicide bombers attacked crowds at Kabul airport, killing several American marines, and leaving an unknown number of Canadians and their families trapped. The withdrawal occurred as Canada and its military allies braced for imminent attack and to allow for the American-led mission to eventually meet its Aug. 31 deadline for departure. The Associated Press reported that U.S. officials said 11 American marines and one navy medic were killed in the attack by a pair of suicide bombers and gunmen in the crowd clamouring outside Kabul airport. It’s not known how many other U.S. personnel were injured. An unknown number of Canadian military personnel stayed behind to assist the American withdrawal, and all were “safe and accounted for” after the Thursday bombing, the Canadian Forces said on Twitter. Canada’s departure, its fiery aftermath, and the concerns about those left behind laid bare …