Why do historians know very little about harappan society today?

first of all, it's important to say that the book we shall not be moved, written by joan dash, is about the first strike of women in the united states in the year 1909. the best historical detail to clarify the reader's undertanding is the phrase "general strike". this strike involved women working at a garment factory who decided to protest   long working hours, low wages and brutal conditions. this strike became known as "the new york shirtwaist strike" or "the uprising of the 20,000". the strike mostly involved jewish women who did not speak english or who had a basic knowledge of the english language. finally, the strike went on from november 1909 until february 1910.