But, it is true that we have been in various forms of "near war" for much of our history.
After the revolution, we were in conflict with both France and England at various times almost continuously, plus we has serious problems with Barbary Coast pirates.
Then we moved west. That movement was accomplished as much by a military campaign of securing our "purchase" of the Louisiana territories as it was just general migration. (Lewis and Clark had military commissions and it was run as an activity of the army). After the civil war there was a long campaign of conquest of "indian lands" (as if some how the rest of it wasn't). These ended, and there was a relative period of time before we began expansion attempts again. These attempts would include Hawaii, the Philippines, and of course the Spanish-American War. There was also the Mexican American War (which should probably be more accurately called the SECOND one. Dunno how one would want to classify the whole "find Pancho Villa" schtick. Then we get to WW I and it's sequel, WWI, Korea, Vietnam, Panama, Granada, Gulf War I, Somalia, Bosnia, Kosovo, Gulf War II, and Afghanistan.
And it should be remembered, that prior to the American Revolution, there was the "French and indian wars". And the reason that the British troops were in Boston, and marching on Concord, is because the Massachusetts Bay colony had been in open and violent rebellion for a year or more. The Boston Massacre wasn't an isolated incident.
There is an interesting book called "A Country Made by War" by Geoffrey Peret that goes into much of this. It also highlights to some extent the effect of our military on our economy (including the fact that West Point trained much of our early men in things like building bridges and canals. Very useful for a country that is rapidly expanding into the industrial age).
http://www.nytimes.com/1989/05/28/books/give-war-its-due.html