The United States has undertaken unilateral and multilateral military operations throughout its history (see Timeline of United States military operations). In the post-World War II era, the country has had permanent membership and veto power in the United Nations Security Council, allowing it to undertake any military action without formal Security Council opposition. With vast military expenditures, the United States is known as the sole remaining superpower after the collapse of the Soviet Union. The U.S. contributes a relatively small number of personnel for United Nations peacekeeping operations. It sometimes acts through NATO, as with the NATO intervention in Bosnia and Herzegovina, NATO bombing of Yugoslavia, and ISAF in Afghanistan, but often acts unilaterally or in ad hoc coalitions as with the 2003 invasion of Iraq.