Backgrounder: Those terrorists that once were "friends" of United States

U.S. President Barack Obama is set to meet with leaders and senior security officials from many other countries at a summit in Washington on Thursday, in an attempt to address the aggravating terrorist violence across the world.

This summit, themed "Summit on Countering Violent Extremism," will be attended by security experts and government officials from Britain and dozens of other countries in light of recent terrorist attacks in Canada, Australia, France and Nigeria.

While the United States would like to consider itself as the leader of the anti-terrorism alliance, its relationship with many extremist groups and individuals is intricate and even questionable.

Among many perilous and brutal terrorist groups in the world which have been backed by the U.S. government, Al Qaeda is the one particularly "exemplary" to show that the U.S. foreign policy is based on realpolitik and the short-term pursuit of narrow interests.

In order to battle against the Soviet's invasion in Afghanistan from 1979 to 1989, U.S. intelligence agencies had backed many Islamic fundamentalist groups in the land-locked country as well as in other Islamic countries.

And soon, one Arabian businessman emerged as the best protege of the Central Intelligence Agency (CIA) of the United States in the surrogate war between the two super powers. His name is Osama bin Laden.

Al-Qaeda, the terrorist group with many of its founders trained by the U.S. government, has become the world's largest and most notorious terrorist group. And its franchises reach almost all war-torn Islamic countries.

As for the Islamic State (IS), which is even "too extreme" in the eyes of regular al-Qaeda fighters, its key members were trained by the CIA and the Special Forces command at a secret camp in Jordan in 2012, according to RT, citing informed Jordanian officials.

What's more, the footsteps of U.S. intelligence agencies are not limited in the Islamic world.

In the 1990s, U.S. special forces and Drug Enforcement Administration worked with a Colombian vigilante group -- Los Pepes -- to track down and kill drug lord Pablo Escobar. The two main leaders of Los Pepes were Don Berna and Fidel Castano, both former employees of Escobar.

In 1997, some of Los Pepes' leaders co-founded the United Self-Defense Forces of Colombia, more commonly known as AUC which was responsible for numerous massacres and political assassinations in Colombia.

In the 1960s, the CIA also trained and harbored two terrorists trying to assassinate Cuban leader Fidel Castro and to topple the communist government in the country.

Luis Posada Carriles, a Cuban citizen who fled to the United States after the Cuban Revolution, helped organize the Bay of Pigs invasion, and after it failed, he became an agent for the CIA.

He was trained at Fort Benning, a U.S. Army post outside Colubus, Georgia. From 1964 to 1968, he was involved in a series of bombings and other anti-Castro covert activities.

Posada was found guilty by a court of Panama as one of the perpetrators behind the 1967 bombing of a Cuban airliner that killed 73 people. But he lived in the United States as a refugee and was never convicted with any criminal activity there.

Posada's accomplice Orlando Bosch Avila, also a Cuban exile, was granted shelter by the U.S. government as well, though former U.S. Attorney General Dick Thornburgh called him an "unrepentant terrorist."

As the United States upholds the flag of anti-terrorism once again, it may have to abandon its selfish and short-sighted interests first. Endi