The Idea, as you will find... «Philosophy: A Very Short Introduction»

The Idea, as you will find if you ever read Hegel's Logic (but be warned, it is desperately hard work), always develops through the conflict of opposed concepts followed by their resolution, which itself turns out to harbour another opposition, upon which a further resolution follows, and so on until the entire system is complete. So it is, therefore, in the political sphere. Conflict issues in a new order, but before too long the new order itself is showing strains; the seeds of the next conflict were already present in it, and once they mature it is swept away in its turn. You may find the metaphysics with which Hegel underpins all this extravagant, wild, and woolly, but when he applies it to human history the result certainly isn't stupid. It is this idea of progress arising out of conflict which is known as ‘dialectic’. It pervades the thought of Hegel, but equally that of Marx, which is why Marx's philosophy is often called ‘dialectical materialism’.