NPT?

Do you know what NPT stands for? And what does it mean?
Today I read the first chapter of '国際機構の政治学.'
It is because a teacher in a political class assigned reading it and writing book review by June 10.
I have to hurry up -_-;

By the way, NPT stands for 'Nuclear Non-Proliferation Treaty.'
Although I had not paid much attention to NPT or IAEA, I think I need to understand them or nuclear weapons proliferation problems.　
NPT is a treaty to prevent the use of nuclear weapons or materials. Now 190 parties have joined the Treaty according to United Nations web page.(http://disarmament.un.org/wmd/npt/index.html)
The United States, the United Kingdom, France, Russia, and China have declared that they have nuclear weapons. In contrary, four countries such as India, Israel, Pakistan, and North Korea do not sign in.
What I have learned by reading the book is that nuclear weapons are very effective to maintain international relations although it is a massively destructive weapons in the world. Thanks to its terrifying destructive power, each country are afraind of conducting nuclear attack. In short, some nations have nuclear weapons to protect themselves and ro gain power in international community. That is why nuclear problem are included in in international relations.