Taft and his Secretary of State, Philander Knox, instituted a policy of Dollar Diplomacy towards Latin America, believing U.S. investment would benefit all involved, while diminishing European influence in regions where the Monroe Doctrine applied. The policy was unpopular among Latin American states that did not wish to become financial protectorates of the United States, as well as in the U.S. Senate, many of whose members believed the U.S. should not interfere abroad. No foreign affairs controversy tested Taft's policy more than the collapse of the Mexican regime and subsequent turmoil of the Mexican Revolution.