By Fareed ZakariaNEW YORK ― The controversy over the desecration of copies of the Koran in Afghanistan and the murder of Americans that followed is, on one level, one moment in a long war. But it also highlights the difficult and ultimately unsustainable aspect of America's Afghan policy.President Obama wants to draw down troops, but his strategy remains to transition power and authority to an Afghan national army and police force as well as to the government in Kabul, which would run the country and its economy. This is a fantasy. We must recognize that and pursue a more realistic alternative.The United States tends to enter wars in developing countries with a simple idea ― modernize the country, and you will solve the national security problem. An articulation of that American approach came from none other than Newt Gingrich during a 2010 speech at the American Enterprise Institute.We are failing in Afghanistan, Gingrich argued, because "we have not flooded the country with highways, we haven't guaranteed that every Afghan has a cell phone, we haven't undertaken the logical steps towards fundamentally modernizing their society, we haven't developed a program to help farmers get off of growing drugs."Now, assuming that every Afghan got a cell phone and could travel on great highways, here is what would not change: The Afghan national government does not have the support of a large segment of its population, the Pashtuns. The national army is regarded as an army of Tajiks, Uzbeks and Hazaras ― the old Northern Alliance that battled the Pashtuns throughout the 1990s.And, simply put, Afghanistan's economy cannot support a large national government with a huge army. (The budget for Afghan security forces is around $12 billion. That is eight times the amount of the government's annual revenue.)As America has discovered in countless places over the past five decades, there are problems with the nation-building approach.First, it is extremely difficult to modernize a country in a few years.Second, even if this were possible, the fundamental characteristics of that society ― ethnicity, religion, and national and geopolitical orientation ― would persist.In Iraq, the United States believed it had an opportunity to remake the country into a model pro-Western democracy. It went in with grand ambitions and an unlimited budget. Today, Iraq has become a Shiite-dominated state that has systematically excluded Sunnis, driven out almost all Christians, and tilted its foreign policy toward Iran and Syria. The Kurds have effectively seceded, creating their own one-party statelets in the north. Iraq is much, much better off than it was under Saddam Hussein's rule, but the country has developed along the lines of its history, ethnicity and geopolitics, not American ideological hopes.We need to come to terms with Afghanistan's realities rather than attempting to impose our fantasies on it. This means recognizing that the Afghan government will not magically become effective and legitimate ― no matter how many cell phones we buy or power lines we install. Because they represent many Pashtuns, the Taliban will inevitably hold some sway in southern and eastern Afghanistan. More crucially, we will not be able to stop Pakistan's government from maintaining sanctuaries for Taliban militants.Accepting reality in Afghanistan would not leave America without options. Even with a smaller troop presence, we can pursue robust counterterrorism operations. We will be able to prevent the Taliban from again taking over the country. The north and east ― populated by Tajiks, Uzbeks and Hazaras ― will stay staunchly opposed to the Taliban.We should support those groups and, more crucially, ally with the neighboring countries that support them. The natural, and historic, allies of the Northern Alliance are India, Iran and Russia; they have permanent interests that will keep them involved in the region. We should try to align our strategy with those countries' strategies (obviously, the alignment will be tacit with Iran).The United States could, of course, maintain its current approach, which is to bet on the success of not one but two large nation-building projects. We have to create an effective national government in Kabul that is respected by all Afghans, whatever their ethnicity, and expand the Afghan economy so that a large national army and police force are sustainable for the long term.To succeed, we would also have to alter Pakistan's character to create a civilian-dominated state that could shift the strategic orientation of the Islamabad government so that it shuts down the Taliban sanctuaries and starts fighting the very groups it has created and supported for at least three decades. Does anyone really think this will happen?