Amendments to the United Nations Charter
Because Charter amendments require the consent of all five permanent members of the United Nations Security Council—defined in Article 23 of the Charter as "The Republic of China, France, the Union of Soviet Socialist Republics, the United Kingdom of Great Britain and Northern Ireland, and the United States"—it is impossible for other UN member states to force the permanent five to give up their Security Council 'veto power', by means of a Charter amendment. Many reformers have described this situation as a Catch-22. According to Global Policy Forum, "the P-5 are content with the present arrangements and oppose any changes that might dilute or challenge their power or expand their 'club.' China has already announced it will block permanent membership for Japan, and the United States has suggested that it will only support Council reform that commands an implausibly 'broad consensus'".
United Nations Security Council
The five permanent members of the Security Council were the victorious powers in World War II and have maintained the world's most powerful military forces ever since. They annually topped the list of countries with the highest military expenditures. In 2013, they spent over US$1 trillion combined on defence, accounting for over 55% of global military expenditures (the US alone accounting for over 35%). They are also among the world's largest arms exporters and are the only nations officially recognized as "nuclear-weapon states" under the Nuclear Non-Proliferation Treaty (NPT), though there are other states known or believed to be in possession of nuclear weapons.