18 years, with the war in Afghanistan being the longest war in American history

 After the 2020 U.S presidential election, then-President Donald Trump announced plans to withdraw U.S. troops from Afghanistan. Trump had made a campaign promise to bring U.S. troops home from "endless wars" and it seems that this was an action towards fulfilling that promise.

The U.S. had been involved in Afghanistan for more than 18 years, with the war in Afghanistan being the longest war in American history. By the end of the year 2020, there were around 4,500 US troops were in Afghanistan and there were talks of a significant reduction to that number. The timeline for the withdrawal, however, was not specified.

Critics of the decision warned that a hasty withdrawal could lead to a resurgence of the Taliban and instability in the region, while supporters of the move argued that it was time for the Afghan government to take responsibility for their own security.

The withdrawal of troops from Afghanistan is a complex process and it would depend on multiple factors, also the withdrawal from Afghanistan was not as fast as it was announced, as it was conditioned on the Taliban meeting certain conditions such as cutting ties with al Qaeda and other terrorist groups, and reducing violence in the country.

It's important to note that my knowledge cut off is in 2021, and it is possible that the situation has changed since then, and the outcome of the withdrawal is still uncertain.