A recent United Nations High-Level Panel identified five categories of threats that we face:
1. Poverty, Infectious Disease, and Environmental Degradation;
2. Armed Conflict — both within and among states;
3. Organized Crime;
4. Terrorism; and
5. Weapons of Mass Destruction.
These are all 'threats without borders' — where traditional notions of national security have become obsolete. We cannot respond to these threats by building more walls, developing bigger weapons, or dispatching more troops. Quite to the contrary. By their very nature, these security threats require primarily multinational cooperation.

Nobel lecture (2005)