Why did USA and its Allies invade Afghanistan in 2001? And why do they stay until now?

Why did USA and its Allies invade Afghanistan in 2001? And why do they stay until now?

this essay was written by a writer, but with weak and unsupported evidence, most of the evidence are not supporting the argument , so i need a professional writer do correct it. if you are really able to put strong evidence please let me know. otherwise it can be refunded. has got an F+ with 37 comments , according to the comments i need complete correction, there are more points that we will discuss later,