The constant paranoia of the 'press the button theory' where an entire city can be leveled with the firing of a nuclear missile. No one likes to feel defenseless under a definite trump card.
I would think it's fear and power. Most likely it's the fear of losing power. Fear is something that motivates most people, and the drive to have power over others (or even over yourself, your surroundings, your country,etc.) There's the need to be the best, to show that you are on top and that you can do it better than everyone else. That's a drive for power.
There's also the fear that if you "so-and-so" has it but you don't, that you're going to get creamed, so why not beat them to the punch and build it bigger and better before they can even try?
I personally think that if more people were driven by respect and love, we would have a lot less war and a lot less death.