Major protests have exploded across the world over the past week, with people taking to the streets in Lebanon, Barcelona and Chile. That's on top of recent demonstrations in Hong Kong, Haiti, Iraq and elsewhere.
So, what makes a protest effective?
Orion Lewis, a professor of political science at Middlebury College in Vermont, studies this for a living. Lewis told The World's host Marco Werman it's not a coincidence all these protests are happening at once.