As American airstrikes began raining down on the de facto capital of the Islamic State in Syria on Monday night, the militant group issued a new installment in its “lecture series” delivered by a British hostage, John Cantlie.

In the propaganda video, Mr. Cantlie is again seated at a table wearing an orange jumpsuit, in a reference to the outfits worn by Muslim prisoners at American detention centers at Guantánamo Bay, Cuba. He reads from a script, explaining how the United States’ involvement in the Syrian conflict will mirror its misadventures in Vietnam.

“In this program, we’ll see how the Western governments are hastily marching towards all-out war in Iraq and Syria without paying any heed to the lessons of the recent past,” Mr. Cantlie says. “Not since Vietnam have we witnessed such a potential mess in the making.”