President Biden on Saturday formally recognized the 1915 mass killing of Armenians by Ottoman Turkish forces as an act of genocide.

Why it matters: The unprecedented designation, which comes on Armenian Remembrance Day, will likely infuriate Turkish President Recep Tayyip Erdoğan, who has previously warned a genocide declaration would harm U.S.-Turkey relations.

• Armenian communities, lawmakers and human rights activists have lobbied for recognizing the mass killing as a genocide for years.
• Biden as a presidential candidate in April 2o2o vowed to make the symbolic designation if elected.
• Previous administrations, including the Trump administration, typically steered clear of the designation to avoid straining relations with Turkey, who is a NATO member and has been seen as crucial to containing Russia and managing issues in the Middle East.

Context: The mass killing occurred when the Ottoman Turks attempted to transport Armenians from eastern Anatolia to the Syrian desert during World War I. Armenians estimate that up to 1.5 million died. Turkey has recognized atrocities occurred during this time, but denies it was an act genocide and says the death toll is exaggerated.

• Former President Reagan in 1981 referenced the Armenian genocide in a statement about the Holocaust.
• The Senate passed a resolution in 2019 that recognized Turkey's genocide of the Armenian people, though the State Department under the Trump administration said the resolution did not formally change the U.S. stance on the issue. The House passed a similar resolution that same year.
• Former President Trump called the mass killings in an April 2019 statement commemorating Armenian Remembrance Day "one of the worst mass atrocities of the 20th century," but he stopped short of labeling them a genocide.

Worth noting: Biden spoke to Erdoğan in a phone call Friday and conveyed his interest in "a constructive bilateral relationship with expanded areas of cooperation and effective management of disagreements," according to a White House readout of the call.