Being an American means taking certain things for granted. Chief among them: A strong military.

Even the most historically illiterate citizen is at least dimly aware that we have a world-class fighting force that protects America and its allies from some very serious threats — one that, among other things, defeated Nazi Germany and Imperial Japan, held back the Soviet Union during the Cold War, and hounded today’s terrorist groups.

In short, we’re safe. We always have been, and we always will be. Right?

It all depends, to be perfectly frank.

Mind you, that’s no commentary on the bravery and dedication of the men and women in today’s military. They do a terrific job, and we should be very proud of them.

The real problem is that they’ve been ill-served by their bosses in Congress. They’ve been underfunded and overstretched for far too long now.

You can get all the sobering details in the 2019 “Index of U.S. Military Strength,” which was just released by The Heritage Foundation. The only non-governmental and only annual assessment of our armed forces, it takes a comprehensive look at each branch, along with the threats we face worldwide.

The bottom line: On a five-rating scale of “very strong, strong, marginal, weak, and very weak,” the overall rating for our military is “marginal.”

When you consider what a vitally important job our military does — one that literally means life or death for hundreds of millions of people here and around the globe — that’s shocking.

But how could it be otherwise? For far too long, we’ve been placing more demands on our troops. They’re in the 17th year of a long war on terrorism — one that, despite its successes, shows no real signs of abating.

Yet until recently, we’ve also been cutting defense spending. That has forced our military, in turn, to cut training. They’ve had to rely on planes, tanks and other equipment that should have been retired years ago.

In other words, we’ve been asking them to do more with less. That’s a formula for disaster.

So how does one best judge the right size, strength and capability of our armed forces? The Index editors use a formula long embraced by successive presidential administrations, Congresses and Department of Defense staffs: the ability to handle two major wars at the same time.

This is why readiness issues rarely become apparent to the public — until it’s too late. It’s like a household living paycheck to paycheck with no savings or line of credit. Everything seems OK until an emergency comes along.

For now, the Index editors say, our military is likely capable of meeting the demands of a single major regional conflict while also taking care of its other ongoing responsibilities. However, they add, “it would be very hard-pressed to do more and certainly would be ill-equipped to handle two nearly simultaneous major regional contingencies.”

Fortunately, things have improved somewhat, thanks to the Bipartisan Budget Agreement of 2018. That helped stabilize funding for this year and 2019.

But, the editors note, “they have not overturned the Budget Control Act that otherwise caps defense spending and that, absent additional legislative action, will reassert its damaging effects in 2020.”

In short, the recent change in funding is a welcome first step. But we’re talking about reversing a trend that is years in the making.

As the editors note: “Without a real commitment to increases in modernization, capacity, and readiness accounts over the next few years, a significant positive turn in the threat environment, or a reassessment of core U.S. security interests, America’s military branches will continue to be strained to meet the missions they are called upon to fulfill.”

Our military serves us well. It’s time for us to return the favor. Let’s ensure they have the funding they need to keep us and our allies safe — not only today, but well into the future.