In a world where great-power competition is intensifying, a revealing test of foreign-policy acumen is a country's ability to avoid costly conflicts or other endeavors that waste resources, divert attention, and ultimately leave them weaker rather than stronger. In other words: staying out of quagmires. Great powers are often happy to see their rivals stumble into strategic quicksand and may even try to encourage such developments, but wise leaders try to stay out of this kind of trouble.

In recent decades, China has done a far better job of avoiding quagmires than either the United States or Russia. Post-Cold War hubris led U.S. leaders to take on a vast array of global responsibilities, some that made sense but many that did not. The "forever wars" in Iraq and Afghanistan are the most obvious examples of the latter, of course, but the United States also gotten itself mired in lesser conflicts in Libya, Yemen, Syria, and various parts of Africa, largely as part of the "global war on terror."

One might add the long, inept, and fruitless effort to broker an Israeli-Palestinian peace, which consumed vast amounts of presidential time and attention and ultimately failed, in good part because Washington acted not as a fair-minded mediator but as "Israel's lawyer." And now U.S. President Donald Trump has walked open-eyed into a quagmire of his own making with Iran, one with few if any benefits, increasingly obvious costs, and no obvious exit save a humiliating retreat.

Similarly, since 2000, Russia has engaged in a series of frozen conflicts with various neighbors, failed to prop up clients such as former Ukrainian President Viktor Yanukovych or former Syrian leader Bashar al-Assad, and is now mired the running sore of war in Ukraine. Not only have these actions cost the Russian economy and the Russian people a great deal, but they have also poisoned relations with most of Europe and made Russia increasingly dependent on China.

Both Washington and Moscow had reasons for acting as they did, but it is hard to argue that these various adventures left either country in a stronger global position.

By contrast, China has stayed out of costly quagmires and focused on building power at home, constructing islands in the South China Sea, expanding its diplomatic presence and influence abroad, insulating itself from foreign pressure by building up stockpiles and reserves, and gaining leverage through its control of raw earths and other parts of global supply chains. To be sure, its growing military power and increasingly assertive foreign policy have alarmed its neighbors and encouraged them to balance against Beijing, but its overall position vis-à-vis both Russia and the United States has improved considerably. China's approach suggests that staying out of trouble abroad is a pretty smart strategy.

So why do states blunder into quagmires, and how might they avoid them in the future? Here are some of the warning signs.

Ignorance. Nobody starts a war that they think will be long, costly, and maybe end with being defeated. It follows that if they had known in advance what they were getting into, most leaders would have tried something else.

And that suggests that quagmires usually arise from ignorance about the country you're taking on, the difficulties you will encounter against them, or the ways that other actors will respond. The lesson: If you're about to intervene in a country that you know very little about, look out.

Bad advice. Decisions to intervene don't arise from thin air; somebody has to come up with the idea and then convince the people in charge to embrace it. If you want to avoid a quagmire, therefore, you should be deeply skeptical of the advice you'll get from self-interested parties who have their own reasons for wanting you to intervene.

It was a mistake for the Bush administration to listen to pro-war Iraqi exiles such as Ahmed Chalabi, who wanted to ride to power on the back of the U.S. military. It was equally foolish for Trump to believe Israeli Prime Minister Benjamin Netanyahu's sales pitch for a war with Iran, or to have paid attention to similar blandishments from pro-war voices in the United States.