In terms of protecting their borders the USA have one to the south with Mexico and one to the north (or east if you're Alaska) with Canada, neither of which seem like likely invaders. Contrast this to other large powers and you'll see they've fairly large borders to protect where invasions seem more likely. Despite this the USA has one of the highest military budgets as a percentage of GDP in the world.

Is this simply to back up a "bigger stick" diplomacy or are there invasion threats I haven't taken into account?


To be clear to those questioning why the comparison is initially around defending USA soil - it isn't that this is all an army is for, but it is definitely part of it. The assumption is that, all else being equal, if a country is in a safer, more defensible position, it wouldn't need to spend as much on defending against invasion. This would mean that its total military budget could be lower. It is just a metric to measure by.

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    I don't know the why exactly, but I guess it's important that all the wars the US has fought in since the american civil war where fought far away.
    – PMF
    Commented Mar 28, 2022 at 15:02
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    This is probably a very popular question and may have come up already. Did you search for it somewhere and what results did you get already? Commented Mar 28, 2022 at 15:23
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    this is a complicated, speculative question, and i'm not sure there's a way to answer it without sounding deeply jaded. are you more interested in the US' cold war self-conception as defender of western liberalism? Do you want to get into the economics of the military industrial complex? do you prefer the 'national virility' conception that's run through far-right nationalism since th 50s? Commented Mar 28, 2022 at 16:00
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    "I searched it on here and didn't get any asking this direct question" I googled the title and got multiple exact copies as first results. @convert "Sure, there are answers on the web, but can they be called objective?" This here would also just be an answer on the web. We ask people to do research, but we don't forbid them to ask if they did research before asking. Commented Mar 28, 2022 at 19:05
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    @PMF Cuba is only 90 miles away from Florida. Commented Mar 29, 2022 at 3:01

11 Answers 11


A lot of this has to do with the geopolitical state of the world. World War II changed a lot for the US. The US had been reluctant to enter World War I.

President Wilson was reluctant to enter World War I. When the War began, Wilson declared U.S. neutrality and demanded that the belligerents respect American rights as a neutral party. He hesitated to embroil the United States in the conflict, with good reason. Americans were deeply divided about the European war, and involvement in the conflict would certainly disrupt Progressive reforms. In 1914, he had warned that entry into the conflict would bring an end to Progressive reform. "Every reform we have won will be lost if we go into this war," he said. A popular song in 1915 was "I Didn't Raise My Boy to Be a Soldier."

World War II, however, saw the US directly involved after the Japanese attack on Pearl harbor. That galvanized the American public towards war (approval hit 97% for entering the war as a result).

After the war ended, the US was in a unique position. The US had the largest military force in the world and it had largely escaped the ravages of war that left Europe having to rebuild for years afterward. In the meantime, the Soviet Union began its political encroachment in Europe, which led to the Cold War, which encompassed the nuclear arms race. It also brought several proxy wars like Korea and Vietnam. During this time, many people of the World War II generation still openly supported having military power to project worldwide (Vietnam was still popular through mid-1967, when mounting losses of drafted men helped changed views).

The recent Russian invasion of Ukraine has underscored why the US still maintains a large standing military. The US does not exist in a vacuum, and if it were to shrink back to defending only its borders, it would likely find itself where it was in World War I: slow to respond until only after a war had started. Germany has recently vowed to increase its military funding, but if Germany were to be attacked by Russia, it would have to heavily rely on NATO for defense, since military expansion takes time. You can't just raise a standing army on a moment's notice.

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    Worth noting that the U.S. was a late entrant to WWII as well, hanging back two years until it was attacked before fully joining the conflict. Also, while it can afford a big military budget due to a large GDP, in terms of active duty military personnel per capita, the U.S. is at pre-WWII level now at a 82 year+ low.
    – ohwilleke
    Commented Mar 28, 2022 at 18:22
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    @ohwilleke I'm not sure active duty personnel is an apples-to-apples comparison, given the changes in technology have significantly changed the cost/utility ratio of training/equipment vs. absolute numbers. Commented Mar 29, 2022 at 14:27
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    @DavidJacobsen Japan is not part of NATO so its policies do not apply. There is a long-standing policy that Japan will not develop nuclear weapons nor allow them on its territory.
    – doneal24
    Commented Mar 29, 2022 at 16:21
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    The extent of Germany's weakness is widely overstated. Even now, Germany's military budget is only $10bn less than Russia's, and unlike other powers - such as Russia, France, and Britain - that spending has been entirely concentrated on national defence rather than developing the ability to project power outside their borders. Commented Mar 29, 2022 at 17:01
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    @JackAidley Well, a lot of the money has gone to McKinsey ... jokes aside, the money appears extremely badly spent -- for which I, as a pacifist, am quite grateful. To all militarists wishing for a strong German military projecting outward: Be careful what you wish for. That the generation who lived through WWII has died does not mean their lessons should be forgotten. Commented Mar 30, 2022 at 14:28

Since Lyndon. B. Johnson's time, the US forces were calibrated to be able to fight 2-"2.5" wars at once. In Bush's time, Rumsfeld articulated that (before 9/11) as

The current strategic doctrine, which Donald Rumsfeld issued in his Quadrennial Defense Review of early 2001 (before the 9/11 attacks), is a package of U.S. military requirements known as 1-4-2-1. The first 1 refers to defending what has since come to be called the homeland. The 4 refers to deterring hostilities in four key regions of the world. The 2 means the U.S. armed forces must have the strength to win swiftly in two near-simultaneous conflicts in those regions. The final 1 means that we must win one of those conflicts “decisively,” toppling the enemy’s regime.

And we saw that during troop surges in Iraq and Afghanistan, over 100,000 troops were sent to each. So in that view, the slightly more than 500,000 army personnel doesn't look so huge.

Of course, there's the large airforce, large navy etc., but the US always wants to easily win in these critical departments, because we know how WW2 was won. (Or Desert Storm etc.)

The US navy too wants to be able to tackle China and Russia simultaneously.

And I'm not sure why you focused only on the threat of US soil invasion. Hopefully you know that the US has committed to jointly defend quite a number of countries, the other 29 countries in NATO (which includes Canada), and some in Asia (to various degree of formal commitment): Japan, the Philippines, Australia, South Korea, and on some level even with South American countries (although quite a few left that alliance--including Mexico).

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    The point of focusing on invasions on USA soil was that, assuming the desire to invade other countries is equal, being in a more defensible position than another country would mean there are lower military requirements for that. So the % of GDP put to military could be lower than countries who need a larger standing army to protect larger more contested borders. Commented Mar 29, 2022 at 8:14
  • Defending against one invader should require less army than invading that same (otherwise) invader. Commented Mar 29, 2022 at 20:49

Not all wars are defensive wars, and defensive wars are not necessarily fought at the land border. Because of this, the number of bordering countries isn't really related to a countries military size.

For defensive wars, see eg the (specious) argument of WMDs in Iraq, or the (valid) entry into WW2.

The US wages non-defensive wars for a number of (purported) reasons, among them fighting proxy wars during the cold war, regime change (either for the good of the US, or the good of other countries (see the 'spreading democracy' argument)), financial benefits, strategical benefits, increasing security (eg fighting terrorism), being a sort of world police, etc.

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    I was really hoping that "world police" link was going to be about the 2004 movie, Team America: World Police :P Or that one of the two words would be that link. Commented Mar 29, 2022 at 4:58
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    "Not all wars are defensive wars, and defensive wars are not necessarily fought at the land border." There is a famous quote by german defense minister Peter Struck: "Deutschlands Sicherheit wird auch am Hindukush verteidigt" - "German security is also being defended at the Hindu Kush". Hindukush in german refers to (half jokingly) the middle east in general
    – SirHawrk
    Commented Mar 29, 2022 at 8:14

There are approximately 800 military facilities owned by the USA around the world. These military facilities are there to control world affairs so that the USA can hold on to its superpower status forever.

The pillars of the USA's superpower status are:

  1. The United States Dollar as a reserve (66% of the world's reserve currency is maintained in the USD) and international trade currency (88% of the world's trade is done in the USD).
  2. The ally community (e.g. GCC, EU, G7, NATO, 5-eyes, ANZUS, etc).
  3. The Petro-dollar system and the petro-dollar recycling system.
  4. The economy of the USA (roughly 23% of the world GDP), and the US-based world banking and financial system (Wall Street, federal reserve system, and SWIFT).
  5. The US tech industry and giant corporations (China has become a titanic challenge in this regard).

If anyone challenges one or more of the five items above, the USA can retaliate in one or more of the following ways:

  1. direct invasion e.g. Vietnam, Iraq, Afghanistan, etc.
  2. indirect invasion e.g. Libya, Syria, etc.
  3. toppling the governments by using local stooges e.g. Iran, Chile, Sudan, etc.
  4. economic sanctions e.g. Cuba, Iran, NK, etc.
  5. Proxy war e.g. Ukraine, etc.
  6. trade war e.g. China, etc.

In order to do the above, the USA needs an enormous military.

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Did Vietnam threaten the position of the USD in international trade?

No. Vietnam was ideological warfare between capitalism and communism.

Did Libya threaten the position of the US tech industry?

No. However, (1) Libya had a nuclear weapons program; (2) Libyan leader Gaddafi was a staunch activist of pan-African currency, and stopped receiving the USD for its oil around 2008; (3) Libya was a model of defying the USA's rules-based international order, and was still a very successful welfare state.

Does the US Navy impose trade bans on China?

No. However, the US government can surveil the sea trade route of China and potentially block it by using its navy during any tense situation.

Probably some parts of the answer could be salvaged by a more oil-specific focus.

I already talked about the petro-dollar system and petro-dollar recycling system.

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    The answer is not wrong in generalities. However, it is hard to call the conflict in Ukraine US retaliation via a proxy war: with or without US support, Ukraine always was going to defend itself in the case of a Russian invasion.
    – Obie 2.0
    Commented Mar 28, 2022 at 22:49
  • @Obie2.0, The answer is not wrong in generalities. --- what do you mean? the answer can't get more accurate than this. whether you like it or not is a different issue.
    – user366312
    Commented Mar 29, 2022 at 3:53
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    Sorry, is that video supposed to demonstrate something other than that the US supported Ukraine over Russia in the conflict over Crimea and the Donbas region? If it is, I must be missing it.
    – Obie 2.0
    Commented Mar 29, 2022 at 4:08
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    This really makes no sense at all. Did Vietnam threaten the position of the USD in international trade? Did Libya threaten the position of the US tech industry? Does the US Navy impose trade bans on China? Probably some parts of the answer could be salvaged by a more oil-specific focus.
    – MSalters
    Commented Mar 29, 2022 at 10:03
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    The dollar is the core of the correct answer to this question. Other answers don't touch it, and IMO are missing the point completely.
    – blud
    Commented Mar 29, 2022 at 17:31

There are some good answers already, but an important aspect has not been stressed yet.

The US has the richest government in the world, with the government having in the order of $10 trillion in annual expenses, nearly twice that of the number 2, China. The US government also has the highest tax revenue in the world.

The US has the largest military expenses in the world because it can afford to have the largest military expenses in the world.

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    But also as percentage of the GDP, military expenses of the US are above the World average. The US spends 4-5% of GDP, the world on average around 2.5%, I think. Being rich, they could spend even less relative to GDP and would still have left over more in absolute numbers than anyone else. Being a super power really is costly. Commented Mar 29, 2022 at 8:14
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    @Trilarion Yes, it's certainly not the only reason, but the other reasons have been sufficiently mentioned in other answers. As a % of GDP, Russia spends even more than the USA, and India and even the United Kingdom are not far behind.
    – gerrit
    Commented Mar 29, 2022 at 8:23
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    Just to drill this point home a bit. This is US military spending as a percentage of GDP. statista.com/statistics/217581/… Commented Mar 29, 2022 at 16:53
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    Also, presumably companies like Boeing, Nothrop-Grunman, and Raytheon lobby congress to keep military spending high, and to have a nation generally oriented toward the military through advocacy, campaigns, etc. Combined with the military being a great way to escape poverty and do something to sort out an errant life, these tend to circle back to an electorate who generally support the intent of that lobbying. To some extent this makes it a (potentially very violent) state-funded cultural and social enterprise.
    – Dan
    Commented Mar 29, 2022 at 18:54
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    @DanSheppard Yes, the military-industrial complex (which is what you describe) is powerful. It was also already mentioned in MetaGurus answer.
    – gerrit
    Commented Mar 30, 2022 at 7:13

By no means the only reason or even the most important reason, but one unmentioned in the discussion is pork barrel spending, which at least seems to be relatively common in the US due to how their legislative and budgetary systems work. For example, the US Congress has been repeatedly criticised for putting funding towards tank programs that even the army doesn't want.

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    I'm guessing "pork barrel" spending is something other than buying barrels of pork for the military? An explanation of that would help this answer. Commented Mar 30, 2022 at 13:37
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    @LioElbammalf The term is well-documented but the short answer is that there many areas of the country have financial interests in either military bases or defense contracting. Politicians are keen to maintain if not expand the associated spending in the district or state they represent.
    – JimmyJames
    Commented Mar 30, 2022 at 16:51

Even in a good neighborhood, security guards are no surprise at a bank or jewelry store. Even in a bad neighborhood, they don't have them at McDonald's protecting Bic Macs.

The USA is one country with 1/20th of the world's population and over 1/5th of the world's wealth. As the first inventors of many modern technologies, Americans started companies that still dominate tech globally. And as a result of World War 2 and all the other historical facts others have mentioned, we ended up developing cutting-edge military technology as well. Our national currency is the most popular reserve currency in the world - control of the USD is valuable. It's not like nobody in the world would ever want to take all of this if we couldn't defend it.

Being geographically isolated was enough security 150 years ago. Look at it from the perspective of a potential conqueror at that time:

  • We were a nation of mostly farmers. Crops are worth a lot, but not a lot per pound, so if you'd like to take them home in your wooden sailing ships it may not be worth your while.
  • You have to get enough troops over here on sailing ships to conquer us. If they need reinforcements, a messenger will need to escape on a sailing ship and reinforcements will arrive at least several months later.
  • Waging war across the ocean would've been hard for us, too. We weren't a threat to anyone.

Now look at it today:

  • Us and our most likely enemies can all drop a nuclear missile pretty much anywhere in the world within an hour.
  • Planes can cross oceans within a day. Military planes are even faster.
  • Ships are slower than planes, but a lot faster, safer, more reliable and higher capacity than 150 years ago.
  • Communication is basically instant between any two points in the world.
  • The USA is a high value target if ever there was one.

TLDR: The world's a small place in light of modern transportation and intercontinental ballistic missiles. The 1800s are over, and being on another continent is not security. And the USA is a high value target.

  • 2
    Some McDonalds do have security guards. wgntv.com/news/chicagocrime/… A search for news articles involving that same block turn up a bunch of violence, so I'm going to guess it is a bad neighborhood. Commented Mar 29, 2022 at 17:46
  • Interesting an compelling take; I appreciate the post and hadn't considered the current-day realities.
    – Aron
    Commented Mar 30, 2022 at 18:19

Is this simply to back up a "bigger stick" diplomacy or are there invasion threats I haven't taken into account?

The former is the correct answer, although one could use many different euphemisms to describe it, depending on the one's attitude towards the US:

  • (factual) The US has such a large military to promote/defend its interests around the world.
  • (detached) To project military force around the globe.
  • (pro-US) To lead the free world.
  • (anti-US) To act as a world policeman.

This is nothing but the extension of the von Clausewitz maxim that "War is the continuation of policy with other means." Although in practice this influence often does not require actually waging a war by simply threatening a war or threatening withdrawing one's military support.

Indeed, it is easy enough to convince oneself that most of the wars that the US has engaged were not posing a threat of invasion of the US mainland - this is likely true even regarding the US involvement in the two World Wars.


All 50 states - and lots and lots of Congressional districts - got (or at least had) some sort of connection to the military; maybe a base, maybe a defense contractor, maybe some other supplier, maybe a secondary/indirect supplier or employer... In any case, this amounts to lots of jobs and lots of tax-revenue...

Few (none!) Congressmen or Senators concerned about their political future would suggest slashing these jobs, or lower the budget making this possible. The result? The world's biggest hammer! And once you got a big hammer, you eventually start looking for upstart nails to hammer down!


The main reason why they have the highest military budgets as a percentage of GDP in the world is just because they are the only one who can afford it. They have the largest of all more or less efficient economies in the world. Many other countries would like to have comparable military spendings and comparable army as well, it is the more the better after all, but that would be too much of a burden for them so the point at which they have to limit themselves is way lower.

  • 1
    Please, consider supporting your statements with figures or references. For example, the statement about the "military budget as a percentage of GDP," if it is true, could be demonstrated with a source and a graphic. While you may think this is common knowledge because of some reading that you have done, the site is not designed for people to discuss conclusions they make based on facts they have internalized. It is important to support your conclusions with your sources.
    – wrod
    Commented Mar 29, 2022 at 18:17
  1. It's 50 different states! Most of the entities you would compare them to are either 1 state or are a much smaller union. Even then it may still be the top 50 states if you simply divided by 50.

  2. The big "free market" Military Industrial Complex. There is a LOT of money to be made.

  3. These 50 states have been doing well for themselves for a long time due in no small part to being two huge oceans apart from the rest of the globe.

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    What does "it may still be the top 50 states if you simply divided by 50" mean?
    – gerrit
    Commented Mar 29, 2022 at 8:01
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    Counting states is a rather irrelevant number. The EU has 27 states, but one of those states (Germany) is itself a Federal state. And the German state of Bavaria is a lot richer than Montana.
    – MSalters
    Commented Mar 29, 2022 at 13:16
  • 1
    It might be more reasonable to refer to total population, GDP, or something like that -- state-count seems fairly arbitrary.
    – Nat
    Commented Mar 30, 2022 at 1:54

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