The only legitimate purpose of the U.S. military establishment is the defense of this country and its people from attack by other countries. It's the job of Congress to implement this principle, by approving funds and passing other laws that regulate the military services. It's also the job of Congress, should it become necessary, to declare war.
Our military establishment has expanded far beyond what is necessary to serve this purpose. Our "defense" budget is now larger than the next five biggest combined -- even though the U.S. represents less than 5% of the world's population, and only about 6% of the land area. There are U.S. bases on every continent. It has become an end itself, consuming a huge amount of resources, adding to the level of taxation and to the national debt.
And if that weren't bad enough, the habit of meddling in the business of other countries has continued to make enemies of people around the world. There hasn't been an actual "declaration of war" since 1942, but Americans have been fighting other people in the name of this country all around the world almost continuously for the past several decades, with every president claiming the power to send them there with or without any specific approval by Congress.
It is up to Congress to put a stop to this, by establishing policies that will make us more secure in a sensible way:
- It is not the job of the U.S. military to serve as "world policeman". People in other parts of the world have the responsibilty for maintaining and paying for the defensive capabilities that are appropriate to their own circumstances. The president should not be permitted to send troops, ships, bombers, missiles, drones, or other forces, or otherwise engage in acts of war on behalf of other countries, unless specifically authorized by an act of Congress or a formal treaty for mutual defense ratified by the Senate.
- The U.S. should not be involved in any way in civil wars – wars between factions / parties / ethnic groups / religious groups within other countries. Americans who believe that one side or the other is deserving of support, or who want to help the victims of war with humanitarian assistance, should be allowed to do that. But the U.S. government should not be taking sides, and the U.S. taxpayers should not be forced to pay for it.
- The U.S. should not enter into mutual defense treaties or otherwise maintain permanent alliances with dictatorships or other totalitarian regimes. Ideally we should be able to defend ourselves without formal alliances with any other country – but to whatever extent alliances turn out to be of practical use in making multiple countries collectively safer more cost-effectively, such alliances should be made only with countries that share our values. To provide support to regimes that don't support our values is to undermine our values – and creates the serious risk that we will end up fighting on the wrong side in a future conflict.