As the battle for the key Syrian city of Manbij grinds into its third month, U.S.-backed forces there have discovered troves of information left behind by the Islamic State. According to Pentagon officials, the documents illustrate how important the city has been to the self-declared caliphate’s operations, specifically as a hub for transiting foreign fighters.

Yet, aside from caches of weapons, communications equipment and troop manifests, U.S.-backed Syrian fighters, known as the Syrian Democratic Forces, have also found evidence that the Islamic State has rewritten school textbooks to promote its violent ideology, said Col. Chris Garver, a spokesman for the U.S. led-campaign in Iraq and Syria.

“They found textbooks that have been rewritten by Daesh to reflect high-end math and science problems, but the word problems are written into pro-Daesh language,” Garver told reporters Wednesday, using another name for the Islamic State.

The Pentagon’s acknowledgment of the group’s educational revisionism is reminiscent of a U.S. effort in the Cold War-era that distributed texts advocating violence in the name of Islam into the hands of Afghan adults and schoolchildren as part of a propaganda campaign to counter the Soviet invasion of Afghanistan.

According to a 2002 report in The Washington Post, the U.S. Agency for International Development gave upward of $50 million to the University of Nebraska at Omaha’s Center for Afghanistan Studies from 1984 to 1994 to produce education programs for the war-torn country. One of the those programs involved supplying textbooks in Afghanistan’s predominant languages of Dari and Pashto, many of which included violent images and text that promoted anti-Soviet sentiment.

The books were distributed with the help of the CIA and Pakistan’s intelligence services through religious schools, known as madrassas. According to New York University Professor Dana Burde’s 2014 book “Schools for Conflict or for Peace in Afghanistan,” many of the textbooks are still in use today, despite efforts to purge them from the region, and they have been republished as updated editions.

Burde writes that the textbooks spanned first through 12th grades and also included “adult literacy lessons” called the “Alphabet of Jihad Literacy.” Burde’s 2011 version of a fifth-grade textbook — a variant of the same text published by the United States in the 1980s — has eight lessons that “glorify violence in the name of Islam.”

One example taken from Burde’s book includes the following:

“For the letter T: Sword (Turra): Ahmed has a sword. He does Jihad with sword. Gun (Topak): My (maternal) uncle has a gun. He does Jihad with a gun.”

According to Burde, as of 2013, Taliban-controlled areas of Afghanistan require schools to use the older U.S.-made texts because “of the way they teach violence as an obligation to religion.”

In 2015, apparent pictures of Islamic State textbooks were posted online, showing some of the same motifs Burde covers in her writing. The Islamic State’s book covers include images of a decapitated Statue of Liberty and one that features masked Islamic State fighters aiming Kalashnikovs.

“Even if a direct link has not been tested for, however, there is strong evidence that using textbooks to create a culture of intolerance and hate is likely to increase public support for militancy,” Burde writes. “Particularly when these messages are framed in religious lessons exhorting young people to engage in violence and defend their faith.”