On October 7, 2001, the U.S. officially started the war in Afghanistan. By the time the last American soldier withdrew from the country on August 30, the war had lasted for 19 years and 10 months, with a total cost of more than $2 trillion, along with the lives of around 2,500 soldiers and 71,000 civilians.

The war may be over, but the aftermath of the longest war in America's history is still echoing, haunting both the American public and the international landscape as more and more questions come up: Why did the U.S. lose? What's next for Afghanistan? And the most fundamental one, why did the U.S. invade Afghanistan in the first place?

What was the real purpose?

The official reason was to counter terrorism. After the Afghan Taliban government refused to hand over terrorist group al-Qaeda's leader Osama bin Laden, mastermind of the 9/11 attack, then U.S. President George W. Bush declared a "war on terror."

According to him, the war in Afghanistan was "a part of the global campaign against terrorism" where the U.S. soldiers acted on justice to defend peace and freedom for "people everywhere to live and raise their children free from fear."

But after the killing of bin Laden in 2011, many started to question the primary mission of the war as the U.S. chose to stay and turned to export its democracy in Afghanistan.

A geopolitical explanation

From the perspective of geopolitics, Afghanistan is located at the crossroad that links Central Asia, West Asia, South Asia and East Asia. Because of that, the country is historically known as the heart of Asia and a vital hub for Eurasia as the whole.

Given its unique strategic position, scholars suggested that the U.S. occupation of Afghanistan is a reflection of Sir Halford John Mackinder's "World-Island Theory." Mackinder, known as the founding father of geopolitics and geostrategy, viewed Eurasia as the heartland that must be taken if one wants to command the world.

Based on the theory, once the U.S. put Afghanistan under its control, Washington would be able to "manage" Eurasia and dominate two of the world's three most advanced and economically productive regions.

Feng Shaolei, director of the Center for Russian Studies at East China Normal University, believes that by controlling Afghanistan, the U.S. can extend its influence to regions such as Central Asia, South Asia and the Middle East so that it can change the original order of Eurasia.

An attempt to export democracy

Apart from geopolitics, Feng also regarded the U.S. occupation of Afghanistan as an attempt to "transplant" the U.S. style of democracy by means of war.

The U.S. destroyed Afghanistan and rebuilt it with Western political systems. By doing so, the Americans hoped to integrate the country into the so-called liberal international order, Feng noted.

Others believe that the U.S. invasion and occupation of Afghanistan is a result of the country's interventionist foreign policy.

In an interview with CGTN, Martin Sieff, senior fellow at the American University in Moscow, said that U.S. foreign policy in the past has acted like a "pendulum" that swings between isolationism and interventionism.

The 20-year war in Afghanistan happened during a period when the U.S. was striving to impose its values and beliefs onto other societies, Sieff said.

He compared the U.S. intervention in Afghanistan to "medieval crusaders in Europe." 

"Their main crusade was against the Muslim world in those days. But if they could not crusade against the Muslims, then they crusaded against Orthodox Slavic Christians in Eastern Europe, and they invaded them instead," Sieff said, adding that the crusader mentality in Washington is directed at China and Russia. 

From the British Empire to the Soviet Union and then to the United States, external forces have dominated the construction of Afghanistan in the past century. They imposed their vision of development on the country and thus, turned the country into a testing ground as well as a mirror that reflects the real situation of the international community.

Now, with the complete withdrawal of U.S. forces, Afghanistan's destiny has finally returned to the hands of its people. Whether Afghanistan can overcome its geopolitical curse and manage to find its own development path is worth watching.