The most significant achievement to emerge from the 2014 Nuclear Security Summit was a pledge by 35 countries to observe the terms of a joint agreement, known as Strengthening Nuclear Security Implementation. This document committed the signatories to incorporate the principles and guidelines of the International Atomic Energy Agency (IAEA) regarding nuclear security into their national laws, and to allow teams of international experts to periodically evaluate their security procedures. Promoted strongly by the chairs of all three nuclear summits-the United States, South Korea, and the Netherlands- the 2014 initiative is an important step towards creating a robust global security system designed to prevent nuclear materials from falling into the hands of terrorists.

Yet China, along with Russia, India, and Pakistan, did not join the pledge. Beijing has not offered any explanations.

China's absence may be due to several reasons: First, China traditionally prefers to formally commit itself to agreements made by international bodies rather than those initiated by individual countries-even though in practice Beijing has followed almost all of the existing international legal frameworks to prevent nuclear terrorism. Second, even if it were willing to offer its political support, Beijing might not have the logistical or technical preparations in place to subscribe to the joint statement. Third, Beijing may be concerned about disclosing sensitive information if it opens its nuclear security arrangements to outside experts