President Jiang Zemin’s visit to the United States in 1997 and President Clinton’s visit to China in 1998 signified improvements in the relationship, but they deteriorated again because of the U.S. bombing of a Chinese embassy in Belgrade, Serbia in May 1999 and the collision between an American reconnaissance aircraft and a Chinese fighter in April 2001. Disagreements over human rights, the status of Tibet, and trade were also destabilizing factors in the relationship.