2.1. source: http://www.defense.gov/Portals/1/Documents/pubs/nuclearweaponspolicy.pdf Two reasons: 1. International security is still unstable and unpredictable. Political intentions might change and the United States need to be prepared. Relationships with Russia have become more complicated since the end of the Soviet Union in the Cold War. 2. Nuclear weapons are not yet relevant to warfare but they will become so and the United State's possession of them allows preparation for future modern military strategy.
3. Who we are
3.1. Started developing atomic bombs in 1939
3.2. Between 1940 and 1996, the U.S. government spent at least $8.8 trillion