The French Revolution, at the end of the eighteenth century, was probably the most abrupt and thoroughgoing change in the habits of a nation of which we have any record. But we shall find, when we come to study it, that it was by no means so sudden in reality as is ordinarily supposed. Moreover, the innovators did not even succeed in permanently altering the form of government; for when the French, after living under a monarchy for many centuries, set up a republic in 1792, the new government lasted only a few years. The nation was monarchical by habit and soon gladly accepted the rule of Napoleon, which was more despotic than that of any of its former kings. In reorganizing the state he borrowed much from the discarded monarchy, and the present French republic still retains many of these arrangements. [Sidenote: The unity or continuity of history.] This tendency of mankind to do, in general, this year what it did last, in spite of changes in some one department of life,--such as substituting a president for a king, traveling by rail instead of on horseback, or getting the news from a newspaper instead of from a neighbor,--results in what is called the _unity_ or _continuity of history_. The truth that no abrupt change has ever taken place in all the customs of a people, and that it cannot, in the nature of things, take place, is perhaps the most fundamental lesson that history teaches. Historians sometimes seem to forget this principle, when they claim to begin and end their books at precise dates. We find histories of Europe from 476 to 918, from 1270 to 1492, as if the accession of a capable German king in 918, or the death of a famous French king in 1270, or the discovery of America, marked a general change in European affairs. In reality, however, no general change took place at these dates or in any other single year. It would doubtless have proved a great convenience to the readers and writers of history if the world had agreed to carry out a definite programme and alter its habits at precise dates, preferably at the opening of each century. But no such agreement has ever been adopted, and the historical student must take things as he finds them. He must recognize that nations retain their old customs while they adopt new ones, and that a portion of a nation may advance while a great part of it stays behind. [Sidenote: Meaning of the term 'Middle Ages.']