BUENOS AIRES — Father Jorge Mario Bergoglio was 39 years old when Argentina’s military junta seized power in March 1976. The seven years that followed were a time of infernal darkness in his country. Union leaders, students, journalists and other left-wing activists were rounded up on the mere suspicion of “subversion.” Many were tortured and raped, or tossed alive from military airplanes into the mouth of the Plata River.