During 1912, Greece,
Serbia,
Bulgaria, and
Montenegro joined in a
Balkan League against the
Ottoman Empire. Fearing a new war in the Balkans, the Ottomans mobilized their armed forces on 14 September and began transferring units to
Thrace; the Balkan League responded in kind. On 30 September, the League presented the Ottomans with a list of demands regarding the rights of its Christian population. The Ottoman Empire rebuffed the demands, recalled its ambassadors in Sofia, Belgrade and Athens and expelled the League's negotiators on 4 October. The League declared
war against the Ottomans, while Montenegro had already began military operations on 25 September. The Greek
Army of Thessaly crossed into Ottoman territory in the early morning hours of 5 October, finding most border posts to be abandoned. The first major clashes took place the following day when the
1st and
2nd Greek Divisions attacked
Elassona, resulting in an Ottoman withdrawal towards
Sarandaporo. At 7 a.m. on 9 October, the Greek infantry began its
assault on Sarandaporo. The 1st, 2nd and
3rd Divisions attacked the Ottoman main line frontally. In the meantime, the cavalry brigade and the
4th and
5th Divisions conducted a flanking maneuver from the west with the intention of striking the rear of the Ottoman positions. The Konstantinopoulos
Evzone detachment struck from the east of the pass. Fearing that they would be encircled by the Konstantinopoulos Evzone detachment, the Ottomans began to withdraw at 7 p.m., towards their second defensive line at Hani 739, under the cover of the night. Upon reaching their second defensive line, the Ottomans became aware of the 4th Division's seizure of Porta Pass, panic spread in their ranks and many soldiers began fleeing and abandoning their equipment. On the morning of 10 October, the 4th Division charged down the northern slope of the Rahovo Mountain, surprising the Ottoman infantry and artillerymen who engaged in a disorganized retreat. At 4 p.m. on 10 October, the 4th Division marched into
Servia, while the Greek cavalry entered
Kozani unopposed the following day. On 13 October, the Greek army transferred its general headquarters to Kozani; a day later King
George I arrived in the city, ordering the army to march towards Thessaloniki and
Veroia. The Ottomans fought a number of small scale delaying actions at Kolokouri, Tripotamos and Perdika, the Greek army nevertheless continued its advance taking Veroia and
Katerini on 16 October. Between 17 and 18 October, the Greek general command forwarded its troops to the Veroia-
Naousa plain. After their defeat at Sarandaporo, the Ottomans augmented the remnants of
Hasan Tahsin Pasha's force with fresh reinforcements. Two divisions from east Macedonia, one reserve division from Asia Minor and one reserve division from Thessaloniki; bringing the total Ottoman forces in the area to 25,000 men and 36 artillery pieces. The Ottomans chose to organize their main defensive line at
Yenidje either because of the town's religious importance for Macedonia's Muslim population or because they did not wish to fight too close to Thessaloniki. The Ottomans dug their trenches at a high hill which overlooked the plain west of the town. The hill was surrounded by two rough streams, its southern approaches were covered by the swampy
Giannitsa Lake while the slopes of
Mount Paiko complicated any potential enveloping maneuver from the north. On the eastern approaches to Yenidje, the Ottomans reinforced the garrisons guarding the bridges across the
Loudias River, the rail line at
Platy and Gida. On 18 October, the Greek general command ordered its troops forward despite receiving conflicting intelligence reports regarding the disposition of the enemy troops. The 2nd and 3rd Greek Divisions marched along the same route towards Tsaousli and Tsekre respectively, both located north-east of Yenidje. The 1st Greek Division acted as the army's
rearguard. The 4th Division headed towards Yenidje from the north-west, while the
6th Division circumvented the city further to west, intending to capture Nedir. The
7th Division and the cavalry brigade covered the right flank of the army by advancing towards Gida; while the Konstantinopoulos Evzone detachment was ordered to seize
Trikala. ==Battle==