The USA has a huge military budget because:
 it values its freedom and independence
 it values its allies and trade routes
 it costs the USA a lot more to get any measure of military might since it does not have a conscripted military and its materiel is not made by government suppliers.
The USA has a huge military budget because:
 it has whipped it's population, and that of a significant portion of the worlds population, into a frenzy of fear and paranoia, by maintaining a permanent war status since the end of WWII. Whether hot or cold, the USA has waged war against non-enemies, aggressively supporting brutal dictatorships around, killing millions in defence of "freedom and democracy" around the world. The USA as "protector" of the "free world" has been holding the human species hostage to the possibility of imminent extinction via nuclear weapons for nearly 70 years now. This in the name of valuing its freedom and independence.
 it has decided that the best social control mechanism for social pacification is to provide the lowest possible cost for goods and promoted consumerism as ersatz status symbols for a largely disenfranchised permanent underclass. In order to secure such cheap access to goods, the USA must dominate all world trade and be able to dictate prices for resources, resource extraction, production and distribution. This in the name of valuing its allies and trade routes.
 it spends a lot less money for the size of our military than any other country would for a similarly sized and scaled military because 18 year-old's with no prospects always form a cheap labor pool( "sold" as in soldier, comes from Roman Latin, daily wage-worker), particularly if one can convince them that they are serving their country men in the name of noble goals and values like "freedom and democracy". And because military production in the USA has always been "dual-purpose", a civilian feel-good, while producing weapons of mass destruction.
The USA has co-opted a tremendously large section of it's so-called private market for dual-purpose: production of disposable goods, while supplying the worlds largest military with an endless production line of "goods", of which no good can ever come. Most major manufacturing firms in the USA would not be economically viable if it were not for this arrangement. Boeing could never make it solely producing commercial air-liners, the market for such is not large enough, but if the Pentagon needs x number of fighter jets, missiles and rockets every year, which must be constantly restocked, due to usage in wars or due to degradation from not ever being used, they can show a profit for their civilian production lines. The same is, and has always been, true for GM, Ford, GE, etc.
The USA has not, historically, HAD a "health service" because we traditionally left health to the people themselves, the private sectore, and communities and states (The US Constitution says nothing about healthcare, and it explicitly says that anything it does not assign to the federal government belongs to the people and to the states)
The USA has not, historically, HAD a health service, because immiseration is a constitutive part of maintaining an exploitable permanent underclass. During the first 250 years of American history, surplus value, ie. profit, was made primarily by either a) stealing the indigenous peoples lands or b) exploiting "free labor", ie. slavery. Following the civil war profit has largely been made by exploiting those born into inter-generational poverty, both here and around the world. The majority of Europeans who immigrated to the USA during the first 150 years of colonization were debt-prisoners, ie. the then european permanent underclass. The USA has proudly cultivated cultural identities for the permanent underclass, going back almost 350 years, nowadays we call them "rednecks", the "n-word", and "mehicans".
The constitution, written for the most part by by the 18th century 1%, actually went to lengths to prevent the existence of a standing army. The USA has been violating it's own constitution every day for nearly 70 years now by maintaining the largest scale military ever seen in world history in direct opposition to our founders intents. With a media hell-bent on scaring the bejesus out of everyone 24/7, covert intelligence services, dedicated primarily to propagating domestic propaganda(be scared, be very scared), and brutal police forces, who routinely terrorize, denigrate and humiliate our permanent underclass, we have held our population in line through domestic terror, knee-jerk reactionary patriotism, dog-whistle ethnic discrimination, and cultural envy as a function of permanently denying the permanent underclass of the USA access to the "freedoms" and "democracy", which supposedly are those things that make America all so great.
Our swollen budgets constantly have been misrepresented to the public. Our government has kept us in a perpetual state of fear — kept us in a continuous stampede of patriotic fervor — with the cry of grave national emergency. Always there has been some terrible evil at home or some monstrous foreign power that was going to gobble us up if we did not blindly rally behind it by furnishing the exorbitant funds demanded. Yet, in retrospect, these disasters seem never to have happened, seem never to have been quite real.
Address to the Annual Stockholders Sperry Rand Corporation (30 July 1957)
[..] the arms trade isn’t really about directly protecting national security. The arms trade is about the transfer of arms from the US, Europe, and Russia to the developing world in exchange for cash, in a process that can empower dictators, fuel wars, and facilitate human rights abuses.
The political policies that are called conservative these days would appal any genuine conservative, if there were one around to be appalled. For example, the central policy of the Reagan Administration - which was supposed to be conservative - was to build up a powerful state. The state grew in power more under Reagan than in any peacetime period, even if you just measure it by state expenditures. The state intervention in the economy vastly increased. That's what the Pentagon system is, in fact; it's the creation of a state-guaranteed market and subsidy system for high-technology production. There was a commitment under the Reagan Administration to protect this more powerful state from the public, which is regarded as the domestic enemy. Take the resort to clandestine operations in foreign policy: that means the creation of a powerful central state immune from public inspection. Or take the increased efforts at censorship and other forms of control. All of these are called "conservatism," but they're the very opposite of conservatism. Whatever the term means, it involves a concern for Enlightenment values of individual rights and freedoms against powerful external authorities such as the state, a dominant Church, and so on. That kind of conservatism no one even remembers anymore.
Yes, we have had disarmament conferences and limitations of arms conferences. They don't mean a thing. One has just failed; the results of another have been nullified. We send our professional soldiers and our sailors and our politicians and our diplomats to these conferences. And what happens?
The professional soldiers and sailors don't want to disarm. No admiral wants to be without a ship. No general wants to be without a command. Both mean men without jobs. They are not for disarmament. They cannot be for limitations of arms. And at all these conferences, lurking in the background but all-powerful, just the same, are the sinister agents of those who profit by war. They see to it that these conferences do not disarm or seriously limit armaments.