Taken from the Reichstag (see Wiki) fire in Germany before World War II which blamed the Polish for burning a German parliament building, however it was a 'false flag' (again, see wiki) operation, covert and conducted by ones own government to be blamed on one or more foreigners to drum up support to declare war against supposed foreign perpetrator(s).
person 1: Did you see this video on YouTube?
person 2: yeah, man. Clearly illustrates how 9/11 was a reichstag. See all the small blasts blowing out lower windows? They're from charges firing to cut support beams so the entire skyscraper will collapse upon itself onto it's own footprint. It's easy to see but some people deny all evidence and think the US government can do no wrong.