The term 'Islamic State' has become firmly entrenched in people's minds. But where did this terrorist organisation come from, what does Al-Qaeda have to do with it, and what role did the United States play? A concise historical review - from the end of the First World War to the storming of Mosul in 2014 - provides answers to these questions. However, this does not require a superfluous flood of facts and figures, but rather a 'common thread' described as simply as possible, which presents a complex topic in an understandable way.