Nineteen U.S.-based historians have protested attempts by Prime Minister Shinzo Abe and his administration to suppress statements in U.S. and Japanese history textbooks about the "comfort women" who suffered under a brutal system of sexual exploitation during World War II.

In a letter to the editor in the March edition of "Perspectives on History," a scholarly journal published by the American Historical Association, the group acknowledges that historians continue to debate whether the numbers of women exploited were in the tens of thousands or the hundreds of thousands, and what precise role the military played in their procurement.

"Yet the careful research in Japan, especially by (Chuo University professor) Yoshiaki Yoshimi, of Japanese government archives and the testimonials throughout Asia have rendered beyond dispute the essential features of a system that amounted to state-sponsored slavery," the letter says.