Well, it should be no surprise that this spills over to Veterans Day. Most of the wars the United States has fought have been unnecessary at best and imperialist at worst.
That starts, of course, with our various wars against Indian tribes. We could have been like Tsarist Russia versus its Siberian aborigines, and simply killed people without the "benefit" of first making treaties then breaking them. That, at least, would have been honest.
Mexican War: Sorry, Texas exceptionalists, but when Tejas was a province of Spain, then of Mexico, its normal boundary was the Nueces, not the Rio Grande/Rio Bravo del Norte. A Congressman named "Spotty" Lincoln was right about President Polk wanting, and pushing for, and conniving for, this war when Mexico refused to sell California, and using Texas issues as the cornerstone of his conniving. Also, El Paso never was a part of old Tejas, either.
Spanish-American War: President McKinley is on record before the 1896 election as wanting the Philippines. Spain requested a third-party investigation of the Maine explosion, arbitration, etc., Nope. We then had a three year imperialist war in those newly-American Philippines after the Spanish-American War itself was done.
World War I: President Wilson was a Britain-leaner far before April 4, 1917. And, the British blockade by extension (blockading Sweden, Denmark, etc., to no more than pre-1914 foodstuffs so they couldn't trans-ship to Germany) was just as illegal under international law as was German submarine warfare. We should have let both sides beat themselves senseless.
Vietnam: "Old hands" in the State Department knew the 2,000 years of Vietnamese-Chinese animosity, and knew that the domino theory was dumb on that account alone.
The Gulf War: I still believe April Glaspie that we set up Saddam Hussein in some way, egging him on in invading Kuwait. Even if we didn't, we have no doorknob-guaranteed right to cheap oil.
There was only one war that we really "underfought" in a sense. That's the Civil War, or actually, Reconstruction. Instead of 20,000 troops in the South for a decade, we should have had 200,000 for a generation, at least.
That said, it's fun to watch and hear "The Battle Hymn of the Republic" sung at Veterans Day and Memorial Day events in the South, since it was a Union-based Civil War song, as stanza 2 makes abundantly clear.
And, for Christians who love to selectively quote Romans 8, you might want to ponder further the issue of "obedience to the governing authorities" in light of both the Revolutionary War and Obamacare. That's you, dominionist Ted Cruz.
Update: I totally agree with this Salon piece.