Across the Arab world, Islamists are the new political power brokers. After decades of repression by secular rulers, they are now poised to transform the region's politics and culture. But it's still not clear what they plan to do with their power, and what that will mean for those who don't share their views. We head to the region to examine how Islamists are beginning to govern. We look back at the history of Islamist movements, and ask how the US should respond to the rapid change sweeping across the Arab world.