On March 26, Obama announced a new nuclear weapons treaty with Russia. He stated that it is "the most comprehensive arms control agreement in nearly two decades" and will cut nuclear weapon production in Russia and the USA by "about a third." The treaty was signed by Obama and Medvedev on April 8 in Prague.
Here's an article and video:
Obama, Medvedev Sign Arms Reduction Treaty: 'An Important Milestone for Nuclear Security'