1969: The Woodstock Music festival took place on a farm outside of Bethel, New York, drawing between 300,000 and 500,000 young people from across the country to hear three days of music from acts including Jimi Hendrix, the Who, the Grateful Dead, Janis Joplin, and the Jefferson Airplane. The event was surprisingly peaceful, given that many more people showed up than anticipated.

Today: Modern marketing techniques have tried to reproduce such a massive event, with no luck.

1969: The largest anti-war demonstration in the history of Washington, D.C., occurred on November 15th, when 250,000 people marched on the capitol. Another 200,000 protesters gathered at the same time in San Francisco.

Today:Lacking outrage at government policies, citizens tend not to band together in such large groups to protest; instead, large demonstrations are often intended to draw attention to areas in which ordinary people can make a difference in their...