In the history of the Serbs and Croats, or of the Serbo-Croatian race, several factors of a general nature have first to be considered, which have influenced its whole development. Of these, the physical nature of the country in which they settled, between the Danube and Save and the Adriatic, is one of the most important. It is almost everywhere mountainous, and though the mountains themselves never attain as much as 10,000 feet in height, yet they cover the whole country with an intricate network and have always formed an obstacle to easy communication between the various parts of it. The result of this has been twofold. In the first place it has, generally speaking, been a protection against foreign penetration and conquest, and in so far was beneficial. Bulgaria, further east, is, on the whole, less mountainous, in spite of the Balkan range which stretches the whole length of it; for this reason, and also on account of its geographical position, any invaders coming from the north or north-east, especially if aiming at Constantinople or Salonika, were bound to sweep over it. The great immemorial highway from the north-west to the Balkan peninsula crosses the Danube at Belgrade and follows the valley of the Morava to Nish; thence it branches off eastwards, going through Sofia and again crossing all Bulgaria to reach Constantinople, while the route to Salonika follows the Morava southwards from Nish and crosses the watershed into the valley of the Vardar, which flows into the Aegean. But even this road, following the course of the rivers Morava and Vardar, only went through the fringe of Serb territory, and left untouched the vast mountain region between the Morava and the Adriatic, which is really the home of the Serb race. In the second place, while it has undoubtedly been a protection to the Serb race, it has also been a source of weakness. It has prevented a welding together of the people into one whole, has facilitated the rise of numerous political units at various times, and generally favoured the dissipation of the national strength, and militated against national organization and cohesion. In the course of history this process has been emphasized rather than diminished, and to-day the Serb race is split up into six political divisions, while Bulgaria, except for those Bulgars claimed as ‘unredeemed’ beyond the frontier, presents a united whole. It is only within the last thirty years, with the gradual improvement of communications (obstructed to an incredible extent by the Austro-Hungarian government) and the spread of education, that the Serbs in the different countries which they inhabit have become fully conscious of their essential identity and racial unity.