Why does the USA have such a large military?

Question

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?

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Edit:

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.

Answer 1

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.

Answer 2

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).

Answer 3

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.

Answer 4

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.

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.

Answer 5

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.

Answer 6

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.

Answer 7

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.

Answer 8

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.

Answer 9

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!

Answer 10

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.

Answer 11

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.