What is controversial about Joe Biden saying “Armenian genocide”?

REPRESENTATIVES OF AMERICA’S government have not always minced their words about the fate that befell Armenians in 1915. At the time, Henry Morgenthau Sr, the American ambassador to the Ottoman Empire, called it “a campaign of race extermination”. Joe Biden is set to describe the killing and mass deportation of Armenians as “genocide”. That is not unprecedented—the last sitting president to use the term was Ronald Reagan in 1981—but it is rare enough to be noteworthy. Mr Biden is sure to anger Turkey’s president, Recep Tayyip Erdogan. Why are events from over a century ago still so bitterly contested?