I was taught the country was originally referred to as the united states of America, small u, small s.
In the Declaration of Independence, the very first official use of the term, it appears as "united States." But using the term as a common noun, not a title.
Of course rules of capitalization were somewhat more fluid back then.
http://www.visualthesaurus.com/cm/wordroutes/the-united-states-is-or-are/