Short Answer 
The U.S. invasion of Afghanistan in response to the 9/11 attacks, led by al-Qaeda, began on October 7, 2001, targeting the Taliban for harboring Osama bin Laden. The swift military response resulted in the Taliban’s quick downfall by November 2001; however, ongoing challenges and instability persisted due to the continued presence of key figures and a lack of lasting peace in the region.
Step 1: Understanding the Invasion Trigger
The invasion of Afghanistan by American troops was initiated in response to the September 11 attacks in 2001, which were orchestrated by al-Qaeda, led by Osama bin Laden. The Taliban government was harboring bin Laden and refused to expel him despite U.S. demands. This refusal prompted the United States to launch military operations on October 7, 2001, under the codename Operation Enduring Freedom.
Step 2: The Swift Military Response
Following the initial demand for bin Laden’s expulsion, American forces, in alliance with the Northern Alliance, commenced aerial strikes against Taliban targets. This collaboration proved effective as military operations led to the rapid downfall of the Taliban government by November 2001. Key actions included:
- Targeted airstrikes on military strongholds.
- Support for ground forces opposing Taliban rule.
- Capture of Kabul, demonstrating military success.
Step 3: Assessing Outcomes and Ongoing Challenges
Although the initial military objectives were achieved with the Taliban’s defeat, significant figures like Osama bin Laden remained at large, resulting in continued instability in the region. The invasion led to over a decade of conflict and challenges in stabilizing Afghanistan. The lack of international support for the Taliban contributed to their rapid fall, but the long-term peace and security in the area has remained a complex issue.