PERHAPS the most useful service a student can do himself A in attempting to study great power co-operation in the years immediately after the Napoleonic Wars is to dismiss from his mind altogether the notion that there ever was such a thing as a Congress System. He may then have some chance of realizing that although there were Congresses after 1815 there was little that was systematic about them. There was no agreement between the powers as to what Congresses were for, and there was no permanent organization for international co-operation such as was set up after each of the two German wars of the twentieth century. Like so many of the 'systems' in history, the Congress System is an invention of historians.