Answer:
Historians label an event as a turning point when it generates very important changes in the course of events. Thus, a turning point breaks with the previous status of the historical moment, from which a new order of events is generated.
Examples of turning points are, among many others, the Battle of Midway in World War II, as it put the Japanese Navy on the defensive for the first time in the conflict; the launching of Sputnik I, since this began the space race in the Cold War; or the attacks of September 11, 2001, since these started the War on Terror that faced the United States against terrorist organizations.