The US dollar declined in value for several reasons, including the Vietnam War, doubts in international markets, and countries needing dollar reserves to purchase oil from OPEC after 1971. Iraq later started selling oil in euros instead of dollars. While the US invasion of Iraq in 2003 reversed this change, the dollar has continued sliding due to concerns over the large US budget deficit and trade imbalance. Foreign purchases of US treasury securities and stocks have helped stabilize the dollar since early 2009, though its value remains dependent on global risk appetite and returns on dollar-denominated assets.