A conclusion should concisely and efficiently summare the points that you have made in your essay. You would then want to clarify your argument. This should be the same line of argument that has been carried throughout the essay, a change in your argument will see the examiner mark you down. To access the marks at that top end you might want to finish the conclusion with an interesting fact or a particularly unique point which you have not made before in the essay: for example when writing about the German unification you may want to finish by reflecting on the militaristic nature of this new country possibly having an impact on the events which were to unfold in the 20th Century.