With contested seas and naval blockades across Montenegro's borders, landing troops and supplies in the Balkans was a difficult process for the allies. A process which only became more difficult with the introduction of Greece into the war on behalf of the Imperial Powers.
Montenegro and its 50,000 men found themselves quickly encircled by the German forces Bruno split off from his main army that equally were greater than ten times the number of defenders. At most, the Allies managed to land a division worth of their soldiers in the region, and that was combined across its many nations.
This division was currently trying their best to gain ground in Greece, where the Hellenic Army was rather incredibly holding its ground for the most part. Outnumbered, and fighting on two fronts, the Serbians and Greeks were in a similar position.