Thanks to Steven Aftergood's post Instances of US Forces Abroad I learned of a new Congressional Research Service report of the same name -- Instances of Use of United States Armed Forces Abroad, 1798-2010 (pdf). From the introduction:
Eleven times in its history the U.S. has formally declared war against foreign nations. These eleven U.S. war declarations encompassed five separate wars: the war with Great Britain declared in 1812; the war with Mexico declared in 1846; the war with Spain declared in 1898; the First World War, during which the U.S. declared war with Germany and with Austria-Hungary during 1917; and World War II, during which the U.S. declared war against Japan, Germany, and Italy in 1941, and against Bulgaria, Hungary, and Rumania in 1942.
Some of the instances were extended military engagements that might be considered undeclared wars. These include the Undeclared Naval War with France from 1798 to 1800; the First Barbary War from 1801 to 1805; the Second Barbary War of 1815; the Korean War of 1950-1953; the Vietnam War from 1964 to 1973; the Persian Gulf War of 1991; global actions against foreign terrorists after the September 11, 2001, attacks on the United States; and the war with Iraq in 2003. With the exception of the Korean War, all of these conflicts received Congressional authorization in some form short of a formal declaration of war. Other, more recent instances often involve deployment of U.S. military forces as part of a multinational operation associated with NATO or the United Nations.
The majority of the instances listed prior to World War II were brief Marine or Navy actions to protect U.S. citizens or promote U.S. interests. A number were actions against pirates or bandits. Covert actions, disaster relief, and routine alliance stationing and training exercises are not included here, nor are the Civil and Revolutionary Wars and the continual use of U.S. military units in the exploration, settlement, and pacification of the western part of the United States.
The report includes 28 pages (!) summarizing over 200 years of US military activities on foreign soil. It's quite a read. For example, the first entry for China reads:
1843: China. Sailors and marines from the St. Louis were landed after a clash between Americans and Chinese at the trading post in Canton.
The first entry for Russia is:
1818: Oregon. The U.S.S. Ontario, dispatched from Washington, landed at the Columbia River and in August took possession of Oregon territory. Britain had conceded sovereignty but Russia and Spain asserted claims to the area.
This is a good resource for military historians.