> We don't blame current political decisions (including stuff like what Isis did) purely on circumstances.

People who study politics absolutely use circumstances to explain political outcomes. Historians discuss the economic impacts of WW1 when talking about the rise of Hitler and Nazi Germany. People discuss the complex political history of the middle east and its long history of resisting superpowers combined with the power vacuum when the US left the region when discussing the rise of ISIS. Power vacuums and food/water scarcity are often the root cause of political instability.

Crazy individuals do crazy things, but those crazy individuals gaining power is always a result of the political system in place at the time.