Former Vice President Joe Biden tweeted on Friday that he will formally recognize the 1915 Armenian genocide if elected president.

Why it matters: President Trump and past presidents have previously avoided the issue, Politico writes. The Senate passed a resolution last December, classifying the event as a genocide. However the Trump administration did not formally acknowledge the event, as such a decision could harm relations with NATO-ally Turkey.

"If we do not fully acknowledge, commemorate, and teach our children about genocide, the words 'never again' lose their meaning. The facts must be as clear and as powerful for future generations as for those whose memories are seared by tragedy. Failing to remember or acknowledge the fact of a genocide only paves the way for future mass atrocities."

— Biden wrote in a Medium post

Context: The mass killing of Armenians occurred when the Ottoman Turks tried to transport them from eastern Anatolia to the Syrian desert during World War I. Turkey claims 300,000 died, but Armenia estimates the number is closer to 1.5 million, BBC reports.

Go deeper: Trump administration says Armenian genocide bill does not change its position