The book is mainly an analysis of capitalism, achieved by critiquing the writings of the leading theoretical exponents of capitalism at that time: these were the political economists, nowadays often referred to as the classical economists; Adam Smith (1723–90) and David Ricardo (1772–1823) are the foremost representatives of the genre.Much of the Critique was later incorporated by Marx into his magnum opus, Capital (Volume I), published in 1867; and the Critique is generally considered to be of secondary importance among Marx's writings. This does not apply, however, to the Preface of the Critique. It contains the first connected account of one of Marx's main theories: the economic interpretation of history. Briefly, this is the idea that economic factors – the way people produce the necessities of life – conditions the kind of politics and ideology a society can have.