ndary defined under Russian arbitration at Petrograd in January
1913--except outside the fortress of Silistria, where strategic reasons
demand its rectification.

It is in the relations of Bulgaria and Serbia, however, that the key to the
Balkan situation is to be found. The Serbo-Bulgarian treaty of February
1912, which formed the groundwork of the Balkan alliance, had limited
Serbia's sphere of influence to northern Macedonia and referred to the
arbitration of the Russian Tsar any disputes arising from conquests to the
south of a certain specified line. Serbia was tacitly given a free hand
in her attempt to reach the sea in Northern Albania. The action of
Austria-Hungary in vetoing her access to the Adriatic forced Serbia to turn
her eyes from west to south and to seek her economic outlet to the sea
down the valley of the Vardar to Salonica and the Aegean. The cession of
Monastir, Ochrida, and the Vardar Valley to Bulgaria would have rendered
this impossible, for it would not merely have driven a wedge between Serbia
and Greece, but would have placed two customs frontiers, the Bulgarian and
the Greek, between Serbia and the sea, instead of only one, the Turkish, as
hitherto. Shut in upon all sides, with all hope of expansion blocked by the
powerful Dual Monarchy to north and west and by a big Bulgaria to east and
south, Serbia would have found herself in a worse position than before the
war. The Bulgarians, intoxicated by their victories over the Turks and
seduced by the promptings of the Austrian tempter, turned a deaf ear to the
arguments of their Serbian allies, and insisted upon their pound of flesh.
They failed to realise that the most effective way of inducing the Serbs to
evacuate Macedonia was to give them adequate backing in their demand for an
Adriatic port. Every fresh intrigue of Sofia with Vienna confirmed Belgrade
in its view of the vital necessity for retaining the Vardar Valley. The
hoary argument that "circumstances alter cases," appeared anew in the garb
of the Bismarckian theory that all treaties are subject to the provision
"_rebus sic stantibus_"--a theory which many great international lawyers
have unhesitatingly endorsed. In this form it appealed as irresistibly to
the Serbs as did the rival shibboleth of "The treaty, the whole treaty,
and nothing but the treaty" to the Bulgarians. It is impossible to absolve
either side from blame; for the Serbs, in formally denouncing a treaty into
which they ha