What is 'class conflict'?

The Comte-Dunoyer thesis, influenced by J. B. Say, was that "ruling class" may be defined simply as that class which manages to rule the State, while the ruled are those dominated by the former through the State. Thus, class conflict does not inhere in the free-market economy or society, but is strictly in relation of State. Class harmony exists only on the free market; class conflict is generated by statism and by the relation of classes to the State.

Source. Couldn't have said it better myself!