I respectfully disagree.
US military spending accounts for 48% of the world's total military spending. (Look it up. http://www.globalissues.org/article/75/world-military-spending#WorldMilitarySpending)
For comparison, US military spending is 5.8 times more than China, 10.2 times more than Russia, and 98.6 times more than Iran.
The US is the world's top arms merchant, sometimes selling to both sides in a given conflict.
The US has military installations in 60+ nations.
The US sometimes literally installs governments and supports many petty dictators and corrupt puppets - in exchange for their loyalty and cooperation.
All this sounds like an empire to me.
But don't believe me. Do some research. Hit wikipedia, google "World military spending", study world history, etc.
If you still believe the US is not an empire, explain why not. Help me understand the distinction. I am willing to give you a fair listen with an open mind.