The manner of the arrival of the Slavs in the Balkan peninsula, of that of the Bulgars, and of the formation of the Bulgarian nationality has already been described (cf. p. 26).  The installation of the Slavs in the lands between the Danube, the Aegean, and the Adriatic was completed by about A.D. 650.  In the second half of the seventh century the Bulgars settled themselves in the eastern half of the peninsula and became absorbed by the Slavs there, and from that time the nationality of the Slavs in the western half began to be more clearly defined.  These latter, split up into a number of tribes, gradually grouped themselves into three main divisions:  Serbs (or Serbians), Croats (or Croatians), and Slovenes.  The Serbs, much the most numerous of the three, occupied roughly the modern kingdom of Serbia (including Old Serbia and northern Macedonia), Montenegro, and most of Bosnia, Hercegovina, and Dalmatia; the Croats occupied the more western parts of these last three territories and Croatia; the Slovenes occupied the modern Carniola and southern Carinthia.  Needless to say, none of these geographical designations existed in those days except Dalmatia, on the coast of which the Latin influence and nomenclature maintained itself.  The Slovenes, whose language is closely akin to but not identical with Serbian (or Croatian), even to-day only number one and a half million, and do not enter into this narrative, as they have never played any political role in the Balkan peninsula.

The Serbs and the Croats were, as regards race and language, originally one people, the two names having merely geographical signification.  In course of time, for various reasons connected with religion and politics, the distinction was emphasized, and from a historical point of view the Serbo-Croatian race has always been divided into two.  It is only within the last few years that a movement has taken place, the object of which is to reunite Serbs and Croats into one nation and eventually into one state.  The movement originated in Serbia, the Serbs maintaining that they and the Croats are one people because they speak the same language, and that racial and linguistic unity outweighs religious divergence.  A very large number of Croats agree with the Serbs in this and support their views, but a minority for long obstinately insisted that there was a racial as well as a religious difference, and that fusion was impossible.  The former based their argument on facts, the latter theirs on prejudice, which is notoriously difficult to overcome.  Latterly the movement in favour of fusion grew very much stronger among the Croats, and together with that in Serbia resulted in the Pan-Serb agitation which, gave the pretext for the opening of hostilities in July 1914.

The designation Southern Slav (or Jugo-Slav, jug, pronounced yug, = south in Serbian) covers Serbs and Croats, and also includes Slovenes; it is only used with reference to the Bulgarians from the point of view of philology (the group of South Slavonic languages including Bulgarian, Serbo-Croatian and Slovene; the East Slavonic, Russian; and the West Slavonic, Polish and Bohemian).