On February 20, 1988, after a week of growing demonstrations in Stepanakert, capital of the Nagorno-Karabakh Autonomous Oblast (the Armenian majority area within the Azerbaijan Soviet Socialist Republic), the Regional Soviet voted to secede and join with the Soviet Socialist Republic of Armenia.
In February 1988, after several episodes of increasingly severe neck pain, Biden was taken by ambulance to Walter Reed Army Medical Center for surgery to correct a leaking intracranial berry aneurysm. While recuperating he suffered a pulmonary embolism, a serious complication. After a second aneurysm was surgically repaired in May, Biden's recuperation kept him away from the Senate for seven months.