what "explosive situation" does mr. herrick claim motivated the school to suspend students for wearing armbands

In the year 1965 three students were expelled from the school because they wore arm bands as they were protesting against the United States that was involved in the war of Vietnam because one student also got killed in this war.

After this situation, students stopped wearing the arm bands. In the year 1969 the supreme court of the United states made an amendment that the schools could not violate the freedom of speech of the students.