The three Slavic allies (Bulgaria, Serbia, and Montenegro) had laid out extensive plans to coordinate their war efforts, in continuation of their secret prewar settlements and under close Russian supervision (Greece was not included). Serbia and Montenegro would attack in the theater of Sandjak, Bulgaria, and Serbia in Macedonia and Thrace.

The Ottoman Empire's situation was difficult. Its population of about 26 million people provided a massive pool of manpower, but three-quarters of the population lived in the Asian part of the Empire. Reinforcements had to come from Asia mainly by sea, which depended on the result of battles between the Turkish and Greek navies in the Aegean.

With the outbreak of the war, the Ottoman Empire activated three Army HQs: the Thracian HQ in Constantinople, the Western HQ in Salonika, and the Vardar HQ in Skopje, against the Bulgarians, the Greeks and the Serbians respectively. Most of their available forces were allocated to these fronts. Smaller independent units were allocated elsewhere, mostly around heavily fortified cities.