The war has consumed the energies of four American presidents - Bill Clinton, George W. Bush, Barack Obama and now Donald Trump. American intervention was allegedly intended to cut off the flow of Al-Qaeda recruits to Europe and to politically stabilize the country.
The accumulative cost of the war in Afghanistan currently stands at US$1.1 trillion since 2001. That's a lot of financial resources that could be used for U.S. domestic purposes such as inner city schools, job creation and health care.
There is an accepted dictum used by military planners to determine the number of counter-insurgency forces necessary to defeat a guerrilla-based army. That formula specifies that there should be a 10:1 ratio between counter-insurgency forces and insurgents. With the Taliban currently having an estimated 25,000-30,000 fighters, it would require that the U.S. put some 300, 000 soldiers into the field to defeat them.
While American military personnel stood at 102,000 in 2011, it has continuously declined and now stands at 13,000 (8,400) people. President Trump has recently announced an additional injection of another 3,900 military personnel.
Afghanistan is now America's longest and most costly war. And like Vietnam it has become "a big muddy," with no strategic objective or purpose. It is a futile war. As the French in Algeria learned and the U.S. in Vietnam, you can win militarily, but lose politically. The war in Afghanistan is lost.