Afghanistan
Afghanistan is not a primitive culture.
Many westerners equate poverty with primitiveness. Afghanistan has very sophisticated cultures that are behind the west in terms of technology but ahead of it in some other important areas.
What some westerners see as "radical" (i.e., Islam) has nothing to do with religion.
The types of acts that are associated with so called "radical Islam" are human reactions that can be induced in any group. If Muslims had adequate control they could easily induce Christians, Hindus, or any other group, to "extremism". There is a history of violent extremism among practitioners of most religions, including Judaism, Christianity, Islam and so on.
Afghanistan is closely associated with Pakistan, but has virtually no link to America.
When America moved large numbers of troops into Afghanistan in 2001 it was essentially invading Pakistan and Saudi Arabia too. This subtlety was lost on most Americans, but it was deliberate.
The purpose of the invasion of Afghanistan was not "to root out terrorists".
Before, during and after the invasion it was clear to anyone who is at all familiar with the region that terrorism would increase as a result of the invasion, not decrease. The simple truth is that "Islamic terrorism" was not a significant problem before during or after the invasion, though the underlying problem did increase as a result of the invasion. There are radical groups in a number of countries, but those groups are almost entirely political extremists using religion as a distraction.
So called "Muslim terrorists" are often no different theologically than nearby groups which are not labelled as "terrorists".
Israel is an example of a place where a disempowered group (Palestinians in occupied or controlled areas) which has been beaten down responds with simple tactics and is labelled a "terrorist group". Only a few miles from these people generally labelled as "terrorists" is another population of Palestinians. Israeli (Arab) Palestinians are a modest number of Palestinians who have been allowed to keep Israeli citizenship. They have access to many of the high paying jobs and good services provided to Zionist Jews, but their number is carefully kept at a level that does not threaten demographics that favor Zionists.
Pakistan, not the United States, has the motive and means to pacify Afghanistan.
If the United States had never set foot in Afghanistan, but simply said to Pakistan's leaders "Solve this problem for us, and send us the bill", the results would have been much better and the costs vastly lower. Primarily, instead of growing dramatically the level of hostility toward the U.S., it would have been reduced.
America's biggest mistake has been ignoring Pakistan's sovereignty.
As a result, America has lost Afghanistan and weakened Pakistan to the point that it's government is likely to take a sharp political turn away from the U.S. very soon.