why the USA are not a democracy?

While that's true in principle, de facto the Anglo-Saxon countries do tend to have two parties that alternate in power, in the US since the 1860s and in the UK since the 1920s (and before that you can go back to the 18th century).

Perhaps it should be put more broadly, saying that countries that inherited their political traditions from Britain tend to have two parties (including Ireland and India for instance). It's not just ex-colonies: two-party Germany and Japan copied the UK in their post-WWII constitutions.

I'm not sure why this should be. I guess it would make a thread on its own.

You have no knowledge, my friend. Ethnics in the USA

white 81.7%, black 12.9%, Asian 4.2%, Amerindian and Alaska native 1%, native Hawaiian and other Pacific islander 0.2% (2003 est.)
note: a separate listing for Hispanic is not included because the US Census Bureau considers Hispanic to mean a person of Latin American descent (including persons of Cuban, Mexican, or Puerto Rican origin) living in the US who may be of any race or ethnic group (white, black, Asian, etc.)

And according to The Economist Hispanics will by 2020 be the majority of Americans.

In the Anglo-Saxon type of government there are two or three dominant - traditional parties. Ex: Republicans - Democrats or Conservatives-liberals-workers' party. You cannot imagine that any other parites can be effective in the government. In the continental European style of government more parties, which can be also very marginal, can be effective at some degree. But I think, in terms of democracy, there isn't a much big difference. As  said in my previous post, especially after the cold war, few parties could present an alternative social and political project. The left wing parties accepted neoliberalism without questioning and they only wanted a softened version of it ( You know the "Third Way" syndrom). Again as I said in my previous post, the representative liberal democracy is in crisis, because you elect your governors within certain boundaries but the vital decisions which determine the world's fate are taken by a few global actors (especially the owners of financial capital). That's why I think that today the concept of democracy is very illusive and deceiving... I mean no more the "demos" rules about the vital issues...