Two of the most important events that involved the media affecting the world were the Vietnam War and the Watergate scandal.
In the Vietnam War, journalists brought the war home to the US. More of the suffering of war was portrayed on television than had ever been seen in 20th century America. The media also did such things as questioning US involvement in Vietnam and releasing the "Pentagon Papers." Such actions helped to reduce popular support for the war.
Watergate would never have been a scandal if not for the media. It was the work of investigative journalists that turned up much of the evidence of the cover-up conducted by President Nixon and his staff. Without this work, it is unlikely that the scandal would have gotten to be so big that the president had to resign.