The military/industrial complex?
The prison/judicial complex?
For example, approximately 0.5% of the NYC population works for the NYPD. So, a tax rate of 0.5% should be sufficient to maintain order in a city like NYC. Add in some overhead and you get to 1%.
Roads are similar, can be done easily for 1% or less.
As a European, I don't think the US would be anywhere as developed and top dog without the "military/industrial complex" ensuring it get its diplomatic way, cheap resources and favorable deals around the world.