The U.S. and its allies are gearing up for a military response against Syrian President Bashar al-Assad’s alleged use of large-scale chemical weapons against his own people in Syria’s ongoing civil war. We take a closer look at the escalating tensions.

The State Department issues a worldwide travel alert and the temporary closure of 19 embassies and consulates. We look at the latest terror threats with Robert Pape, Professor of Political Science at the University of Chicago. View a map of the closures and charts on attacks.

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The FBI says it will go to "the ends of the Earth" to find those responsible for the Boston Marathon bombing. We hear from security and terrorism experts on what clues we know so far, and how agencies plan for similar attacks.

In three days, the largest NATO summit in history will be held in Chicago. Defense funding, Afghanistan, and new partnerships will be at the top of the agenda. We look at what the alliance hopes to accomplish this weekend.