The disastrous Greek defeat in the Greco-Turkish War of 1897 exposed major flaws in the Hellenic Army's organization, training and logistics.

[2] Venizelos followed in Theotokis' footsteps by re-arming and re-training the military, including extensive fortification and infrastructure works, purchase of new weapons, and the recall of reserve classes for training.

[3] After being informed of a Serbo-Bulgarian alliance, Venizelos ordered his ambassador in Sofia to prepare a Greco-Bulgarian defense agreement by 14 April 1912, fearing that should Greece fail to participate in a future war against the Ottomans, it would be unable to capture the Greek majority areas of Macedonia.

The treaty was signed on 15 July 1912, with the two countries agreeing to assist each other in case of a defensive war and to safeguard the rights of Christian populations in Ottoman held Macedonia, thus joining the loose Balkan League alliance with Serbia, Montenegro and Bulgaria.

[5] The Army of Thessaly crossed into Ottoman territory in the early morning hours of 5 October, finding most border posts to be abandoned.

[7] Despite the position being perceived as impregnable by its defenders,[8] the main body of the Greek forces managed to advance deep inside the pass,[7] while auxiliary units broke through the Ottoman flanks.

[11] After their defeat at Sarantaporo, the Ottomans augmented the remnants of Hasan Tahsin Pasha's force with fresh reinforcements[12] and organized their main defensive line at Yenidje (Giannitsa).

On 18 October, Crown Prince Constantine ordered the bulk of the Army of Thessaly to head towards Yenidje despite receiving conflicting intelligence reports regarding the disposition of the enemy troops.

[13] In the meantime, the 5th Greek Division under Dimitrios Matthaiopoulos, continued its advance across western Macedonia, aiming to reach the Kailaria (Ptolemaida)-Perdika area, where it was to await further orders.

[17] The Greek right column initially showed determined resistance but struggled to defend Lofoi and its soldiers fled the field towards Vevi after realizing that it was about to be encircled.

Matthaiopoulos placed his 7,000 infantrymen north-east of the town, the 20 artillery pieces were stationed in the Sotiras village, while 80 cavalry were to protect the western flank of the division at Giouloun.

The Ottomans who had just been defeated at the Battle of Prilep, withdrew most of their troops at Sorovich to Monastir in an effort to halt the Serbian drive towards the city.

[22] Shortly before the dawn of 24 October, a company belonging to the 17th Ottoman Division armed with several machine guns approached the Greek western flank from the direction of the village of Fanos.

By 10:00 a.m., the main body of the Greek force had been routed, fleeing towards Kozani, while the commander of a battalion stationed at Drosopigi led it to Kleisoura after realizing that the battle was essentially over.

Those forces assembled at Edessa on 2 November and were eventually able to seize Florina, yet Monastir fell into Serbian hands after the conclusion of the eponymous battle.