The sudden rise of the militant group known as the Islamic State in Iraq and Syria has prompted a serious effort to make sense of the group’s appeal in the Arab world, the Syrian columnist Hassan Hassan wrote last week.

“Since ISIS took over large swaths of Iraq, in particular, Arabic media outlets of all types have produced reports about the nature of the group and the source of its ideology,” Mr. Hassan wrote in The Guardian. “There is a collective soul-searching in the region, coming from everyone from ordinary people to clerics and intellectuals.”

For instance, the Lebanese scholar Ziad Majed wrote on his blog that at least six factors from the recent history of the Middle East helped give birth to the militant movement, including “despotism in the most heinous form that has plagued the region,” as well as “the American invasion of Iraq in 2003,” and “a profound crisis, deeply rooted in the thinking of some Islamist groups seeking to escape from their terrible failure to confront the challenges of the present toward a delusional model ostensibly taken from the seventh century.”

That sort of introspection is not for everyone, of course, so a popular conspiracy theory has spread online that offers an easier answer to the riddle of where ISIS came from: Washington.