Last weekend, 52 world leaders from countries around the world and four heads of key international organization concluded the fourth and the last Nuclear Security Summit. The summit, first proposed by President Barack Obama in 2009 and followed by three summits in Washington DC in 2010, in Seoul in 2012, and in The Hague in 2014, has largely accomplished its mission, and from now on the global governance of nuclear security will shift from summit format to daily management.

Progress achieved through the four summits is quite impressive. As originally designed, the Nuclear Security Summit is to raise global awareness of nuclear security at the highest level. Without any doubt, the number of world leaders participating in the four summits manifests the importance attached to nuclear security by countries around the world. In the past seven years, more and more countries signed and ratified the key international instrument – the Convention on the Physical Protection of Nuclear Material and the Amendment to the convention adopted in 2005, and it is expected to come into effect very soon. More and more countries are beginning to strictly observe and actively participate in other international agreements and multilateral regimes, such as International Convention on the Suppression of Acts of Nuclear Terrorism, the United Nations Security Council resolutions 1373, 1540 and 1887, the Global Initiative to Combat Nuclear Terrorism, the Global Partnership against the Spread of Weapons and Materials of Mass Destruction. Their support and cooperation with International Atomic Energy Agency (IAEA) and the International Criminal Police Organization (Interpol) reach a higher level as well.

A broader and solid consensus on strengthening nuclear security has been reached, and concrete, tangible steps have been adopted to secure the world's vulnerable nuclear materials. Over the past seven years, 14 nations and China's Taiwan have eliminated entirely the highly enriched uranium (HEU) and plutonium they once possessed. South America is now completely free of dangerous nuclear materials, and Central Europe and Southeast Asia will soon be free of these materials as well. Many countries have strengthened the physical protection of nuclear materials and facilities, and stronger regulations have been put into place. Fifteen Centers of Excellence have been created to promote national and international exchange and cooperation, education and training, which is critically important to boost nuclear security. In addition, major progress has been made in combating illicit trade and trafficking, such as by installing radiation detection equipment at international border crossings, airports and ports, and through regular exercises to intercept potential proliferations. Nations have made hundreds of commitments to improve nuclear security, and most of those voluntary commitments have been implemented as well.