COLCHESTER, Vt. — BY leaking details of the National Security Agency’s data-mining program, Edward J. Snowden revealed that the government’s surveillance efforts were far more extensive than previously understood. Many commentators have deemed the government’s activities alarming and unprecedented. The N.S.A.’s program is indeed alarming — but not, from a historical perspective, unprecedented. And history suggests that we should worry less about the surveillance itself and more about when the war in whose name the surveillance is being conducted will end.