The U.S. is the world's largest arms dealer, and its signing is seen as critical to the success of the Arms Trade Treaty. But many of the other top arms exporters have yet to sign.
Secretary of State John Kerry signed the pact Wednesday, on the sidelines of the U.N. General Assembly. He says it's a "significant step" in keeping the world safe.
Some senators who oppose the treaty contend it could infringe on Americans' rights to bear arms.
Kerry notes that the treaty does not regulate domestic weapons sales.
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