No less important than the physical aspect of their country on the development of the Serbs has been the fact that right through the middle of it from south to north there had been drawn a line of division more than two centuries before their arrival.  Artificial boundaries are proverbially ephemeral, but this one has lasted throughout the centuries, and it has been baneful to the Serbs.  This dividing line, drawn first by the Emperor Diocletian, has been described on p. 14; at the division of the Roman Empire into East and West it was again followed, and it formed the boundary between the dioceses of Italy and Dacia; the line is roughly the same as the present political boundary between Montenegro and Hercegovina, between the kingdom of Serbia and Bosnia; it stretched from the Adriatic to the river Save right across the Serb territory.  The Serbo-Croatian race unwittingly occupied a country that was cut in two by the line that divides East from West, and separates Constantinople and the Eastern Church from Rome and the Western.  This curious accident has had consequences fatal to the unity of the race, since it has played into the hands of ambitious and unscrupulous neighbours.  As to the extent of the country occupied by the Serbs at the beginning of their history it is difficult to be accurate.

The boundary between the Serbs in the west of the peninsula and the Bulgars in the east has always been a matter of dispute.  The present political frontier between Serbia and Bulgaria, starting in the north from the mouth of the river Timok on the southern bank of the Danube and going southwards slightly east of Pirot, is ethnographically approximately correct till it reaches the newly acquired and much-disputed territories in Macedonia, and represents fairly accurately the line that has divided the two nationalities ever since they were first differentiated in the seventh century.  In the confused state of Balkan politics in the Middle Ages the political influence of Bulgaria often extended west of this line and included Nish and the Morava valley, while at other times that of Serbia extended east of it.  The dialects spoken in these frontier districts represent a transitional stage between the two languages; each of the two peoples naturally considers them more akin to its own, and resents the fact that any of them should be included in the territory of the other.  Further south, in Macedonia, conditions are similar.  Before the Turkish conquest Macedonia had been sometimes under Bulgarian rule, as in the times of Simeon, Samuel, and John Asen II, sometimes under Serbian, especially during the height of Serbian power in the fourteenth century, while intermittently it had been a province of the Greek Empire, which always claimed it as its own.  On historical grounds, therefore, each of the three nations can claim possession of Macedonia.  From an ethnographic point of view the Slav population of Macedonia (there were always and are still many