What is the purpose of the military?

I believe we must look to the constitution for the definition of war powers for the military and this document should be the general limits of our powers.

Since WWI & WWII we have moved beyond our originally intended Constitutional limits. This has led to significant engagements outside the United States the framers did not intend. I believe we need to determine some way of limiting ourselves or we will continue to be the world's police force until we run out of economic power to maintain the size of our force.

Based on my reading the military is for common defense and offensive actions when declared by Congress. I believe the intent is to deter war.

Notes:
Note ***I am using the original constitutional text, misspelling is because the common word spelling has changed***

We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, "provide for the common defence", promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.

Section. 8. (Legislature)

***Removed non-defense powers***

To define and punish Piracies and Felonies committed on the high Seas, and Offences against the Law of Nations;

To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;

To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years;

To provide and maintain a Navy;

To make Rules for the Government and Regulation of the land and naval Forces;

To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;

To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;

The final instrument of national power; when the other means have failed or are not suitable.

Doctrine: To Fight and Win our Nation's wars

Deter war through training readiness and presence

I think you are right on target. I will also add in this day and age that are role is continually evolving. The days of rolling across continents hopefully ended with WWII. From Korea through Panama we seemed to diminishing the scale of our conflicts but then Desert Storm OEF & OIF hit and we took an upscale turn in both size and duration. I think we still serve as a deterrent to conventional forces but terrorist forces, "peacekeeping"/belligerencies will always be a challenge to us IMHO a) because our goal is never to stoop to either their level of terror (beheadings and the like) or to their demands and b) we're (conventional units) designed to work as a cohesive and interdependent "force" not as cells which is what the SPECOPS community is trained for.

To break stuff and kill people in the service of enforcing our foreign policy.

To be succinct: our job as members of the US military is to preserve, protect and defend the Constitution of the United States against all enemies, foreign and domestic; and to bear true faith and allegiance to the same. We defend our nation and our way of life, responding as ordered by those elected or appointed over us. There is a moral consideration, but it has nothing to do with the international community or our standing as "members of the human race." The international community, and the rest of the human race, are always our rivals, and often our enemies. If there is a moral issue, you have the right, and I argue, the responsibility to resign your commission and make a stand in the public arena.

Wow Paul, what a heady question for RallyPoint. Lots of good answers below too... I'll take a shot and see if I can keep it to a minimal number of words.

---To strengthen our country.---

There, I got it down to four words, but then you have to unpack it just like any of the references to the Constitution below by getting yourself "5 whys" deep in many directions. Here's my meditation.

Why 1: Why does a country require military strength. Answer-- see Thucydides or Clausewitz or any number of the founding documents and our nation's history.
Why 2: Why does strength necessarily entail military strength? Answer-- It does because warfare tests human faculties and capabilities-- all of them.
Why 3: Why do we have to test our human faculties and capabilities? Answer-- Strength requires the constant exercise, learning, and adjustment that only militaries can provide on a national scale.
Why 4: Why are militaries the only enterprises that can provide for the testing of our human faculties and capabilities? Answer-- because they involve, potentially, the life and death struggle necessary to sharpen our human potential.
Why 5: Why aren't other enterprises (like business or sport) equal tests and cauldrons for testing and refining our human metal to make our country strong? Answer: Because these enterprises do not require the selflessness that the military and defense of a strong country do.

I think about this a lot because the military is all I've done since 17 years of age. Have I spend my life unwisely? In pursuit of an inherently destructive enterprise for humanity? I don't think so for the reasons above. The military is absolutely necessary for the strength of our country-- and incidentally-- for the betterment of human kind through a government that is based on America's values.

The Navy and the Air Force justifiably have gotten a lot of "purpose" mileage out of securing the global commons. This isn't anywhere in the oaths, per se, but is implied in the constitution, see below. By the verbiage, the Army has taken up some of the responsibilities of the militia through the Reserve Component. I think the true purpose is more simple... "war is the continuation of politics by other means." - Clausewitz

"To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;

To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years;

To provide and maintain a Navy;

To make Rules for the Government and Regulation of the land and naval Forces;

To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;

To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;"

http://www.archives.gov/exhibits/charters/constitution_transcript.html

To defend and protect the constitution and the American people from all enemies foreign and domestic