The education ministry issued a notice earlier this month to advise teachers to be careful about "inappropriate" supplementary materials. The intent was clearly to caution teachers about departing too far from the decided views inside public school textbooks. For the past 40 years, the education ministry has never commented on materials, so this warning is a significant new approach to controlling the content being taught.
The directive from the ministry follows closely on the attempt by the Abe administration to control passages about Japan in American high school textbooks. The mistaken idea that the Japanese government should control what historical concepts, facts and approaches are to be taught in other countries is the context for the notice given to Japanese teachers.
Of course, the Japanese education ministry cannot fire American high school teachers who do not agree with its view of history, society or other controversial topics. But the Abe administration seems intent on promoting certain views by warning teachers inside Japan. The ministry has long been concerned about what content is included in textbooks.