How has the world changed?

What's different about the world in the wake of last week's Nuclear Security Summit, Rachel Maddow asked Joe Cirincione.

First, said Joe, President Obama "forged international recognition that nuclear terrorism is the number one threat facing most countries."  Two, the countries have committed to a plan of joint action.  The third significant change is "that they have agreed to come back in two years to hold themselves accountable, to secure all loose nuclear material in the world within four years.  You do that, you stop Osama Bin Laden.  You do that, you prevent nuclear terrorism.  You fail to do that, and one of the capitals represented at the summit will go up in a mushroom cloud." 

Watch the segment here:

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