Interestingly (to me at least) the equally well-attested massacre of 1.5m Armenians by the Turks is not recognised as genocide by the UK government and the European Court of Human Rights ruled that it was not a crime to deny the massacre had taken place.
Read Robert Fisk's 'Great war for civilisation' (probably a bit lefty for some). It's a wonderful if not depressing history of the modern Middle East and coves the Armenian genocide very well.