WASHINGTON—President Joe Biden has formally recognized that the systematic killings and deportations of hundreds of thousands of Armenians by Ottoman Empire forces in the early 20th century were “genocide”—using a term for the atrocities that his White House predecessors have avoided for decades. With the acknowledgment, Biden followed through on a campaign promise he made a year ago Saturday—the annual commemoration of Armenian Genocide Remembrance Day—to recognize that the events of 1915 to 1923 were a deliberate effort to wipe out Armenians. Biden used a presidential proclamation to make the pronouncement. While previous presidents have offered somber reflections of the dark moment in history via remembrance day proclamations, they have studiously avoided using the term genocide out of concern that it would complicate relations with Turkey—a NATO ally and important power in the Middle East. But Biden argued when making the campaign pledge last year that failing to call the …