Empires rise and fall; they do not last. In the eyes of many, the US exerts the strongest destabilizing influence on world events, and thus presents the greatest threat to world peace. World power #1 hasn't acquired this top position by chance. Since 1945, no other nation has bombed as many other countries or toppled as many governments as the US. It maintains the most military bases, exports the most weapons, and has the highest defense budget in the world.
USA: The Ruthless Empire explains the background factors, motives, and resources of this world power.