The stir caused by a textbook’s descriptions of the mass lynching of Koreans following the 1923 Great Kanto Earthquake has prompted Yokohama’s board of education to order schools to collect the books from students.

In an unprecedented move, the board ordered municipal junior high schools to recall the 2012 edition of the book, a supplementary text, saying the use of the word “massacre” “can cause a misunderstanding.” The term has also been criticized by some historians.

Immediately after the Sept. 1, 1923, earthquake in the Kanto region, unconfirmed rumors spread that Koreans were rioting and committing acts of sabotage. Based on the rumors, the army, police and vigilantes killed many Koreans, as well as Chinese and Japanese mistaken for Koreans. It’s unclear because of the chaos how many were killed, but it’s thought the slayings topped 6,000 in Tokyo and Kanagawa Prefecture alone.

Previous editions of the text, titled “Wakaru Yokohama” (“Understanding Yokohama”) and edited by the board, said “some members of the vigilante corps killed Koreans.” The book was first published in 2009.

However, the edition distributed in May 2012 states that “the military, the police and vigilante groups persecuted and massacred Koreans.” It also shows a picture of a cenotaph erected by Japanese as an expression of apology.

The revised entry made media headlines at home as well as in South Korea and China.

In July 2012, a municipal assembly member from the Liberal Democratic Party took up the issue during a session, saying: “It could affect historical concepts in our country and diplomatic relations. It is not a matter only for Yokohama.”

The board of education’s chairman at the time pledged to revise the edition and recall the books already distributed.

The board later reprimanded the person in charge of the revision, criticizing the decision-making process as inappropriate. The 2013 edition reinstated the description and a recall was begun of the 2012 version.

The board also twice instructed school principals to collect all the books and ask students who did not obey their reasons why.

On Wednesday, historians submitted a petition to Yokohama asking that the decision to recall the books be reversed.