Henry Kissinger has noted that in his adult lifetime, the United States has fought five major wars and began each one with great enthusiasm and public support. But in all of them, Americans soon began to ask, "How quickly can you withdraw?"
In three of these conflicts, he says, the United States withdrew its forces unilaterally. Today we are watching a similarly powerful, and understandable, enthusiasm for an expanded war against the Islamic State. Let us try to make sure we understand what it would entail not just to start it but also to end it.
One place to learn some lessons might be from a strategy that has been relatively successful — the war against al-Qaida. As Peter Bergen noted in 2012, a year after Osama bin Laden's death, the group's leadership had been destroyed, its resources had disappeared, and its support among the Arab public had plummeted.
It has not been able to launch an attack on Western soil since the London bombings 10 years ago.
The picture did not always look like that. After 9/11, officials and experts spoke of al-Qaida with the awe and fear they now reserve for the Islamic State.
Once the U.S. and its allies began battling the group, it inspired or directed several attacks across the globe, including the bloodiest in the West since 9/11, the Madrid train bombings, which killed 191 people.
But those attacks did not mean al-Qaida was "winning" the war on terror any more than the attacks in Paris last week mean that the Islamic State is winning.
In fact, it's possible that as it loses territory on the ground, it is resorting to terror abroad.
What explains the success against al-Qaida? Many experts point to the genuinely global counterterrorism operations, especially the sharing of intelligence. Others note the fact that the group overplayed its hand in Iraq.
In one of the best books on the topic, "Hunting in the Shadows," Seth Jones concludes that whenever the U.S. adopted a "light-footprint strategy" — special operations, covert intelligence and law enforcement — it did well. Whenever the U.S. and its allies sent troops into Muslim countries, he notes, "al-Qaida has benefited through increased radicalization and additional recruits."
This is why from the start, the Islamic State has sought to bait Western countries into sending troops to Syria.
Defeating the group militarily would not be difficult. But to keep it defeated, someone would have to rule its territories or else it, or a variant, would just come back. The Islamic State draws its support from Sunnis in Iraq and Syria who feel persecuted by the non-Sunni governments in both countries.
In addition, the group has created a functioning state that provides some measure of stability for a population that has been battered over the last decade.
In this sense, the Islamic State is more akin to the Taliban than to al-Qaida, which was a gang of foreigners lodged in Afghanistan as guests of the Taliban. But the Taliban itself is a local group, with support in the Pashtun community of Afghanistan and Pakistan.
This explains why the U.S. has not defeated it, after 14 years of warfare and tens of thousands of American soldiers and now many more Afghan troops. Keep in mind that in Afghanistan, the U.S. has a decent local ally that has considerable legitimacy. In Syria, it has none. The Kurds are a crucial ally, and should become even more important in the months ahead. Still, as an ethnic minority, they cannot govern Arab lands.
Politicians call on America to build up an army of moderate Syrians. It is a worthwhile endeavor. But historically, when foreigners have helped put together local forces, those forces usually lack legitimacy and staying power — think of the Cubans who landed at the Bay of Pigs, the South Vietnamese regime, or Washington's favored Iraqi exiles.
This essential problem — the lack of a credible local ally — makes ground operations in Syria harder than Iraq, Afghanistan or Vietnam.
This is not to counsel despair but to suggest "strategic patience," as President Obama rightly says. The Islamic State is not nearly as strong as the hysteria of the moment suggests. It is surrounded by deadly foes.
Many countries are fighting against it — from Sunni Saudi Arabia to Shiite Iran, from the U.S. to Vladimir Putin's Russia, from neighboring Jordan to faraway France. Its territory is shrinking and its message is deeply unpopular to most in its supposed "caliphate" — witness the hundreds of thousands of Syrian refugees fleeing its barbarism.
Counterterrorism, intelligence, airstrikes, drones and special operations are arenas where the West has the advantage — it has the money, technology, know-how and international cooperation. And it can hammer away for months, even years.
If instead, panicked by terrorism, we were to send American soldiers into the deserts of Syria, we would enter the one arena where the Islamic State has the decisive advantage. And after a few inconclusive years, people would start asking, "How quickly can you withdraw?"
Fareed Zakaria hosts CNN's "Fareed Zakaria GPS," and makes regular appearances on shows such as ABC's "This Week" and NBC's "Meet The Press." He has been editor at large at Time magazine since 2010, and spent 10 years overseeing Newsweek's foreign editions. He is a Washington Post (and internationally syndicated) columnist. He is author of: "The Post-American World." For more of Fareed Zakaria's reports, Go Here Now.