They were committed by local Greek and Armenian bands with the invading Hellenic Army,[1][6] against the Turkish Muslim population of the Yalova Peninsula.

[2] In an Ottoman inquiry of 177 survivors in Constantinople, the number of victims reported was very low (35), which is in line with Toynbee's descriptions that villagers fled after one to two murders.

[11] An Inter-Allied commission, consisting of British, French, American and Italian officers,[a] and headed by Maurice Gehri, the representative of the Geneva International Red Cross, and Arnold Toynbee went to the region to investigate the atrocities.

[3] After World War I, the Ottoman Empire officially surrendered to the Entente Powers and it had to disband its army.

At the peace conference the British and French tried to secure territory for the Kingdom of Greece in Smyrna and its surrounding regions.

During its retreat (August–September 1922) the Greek army carried out a scorched-earth policy and laid waste to many Turkish cities and villages and committed massacres against its inhabitants.

An additional factor that lead to violence was the return of Greek refugees to their homes, who had been dislocated as a result of the Ottoman ethnic cleansing policies during World War I.

[17] On the other hand, thousands of Turkish refugees from the Balkan wars, who had occupied their homes in the meantime, were expelled.

This turn of events created a rural proletariat apt for brigandage and violence by irregular groups.

[17] According to a report of the Allied commission the events during World War I and the problems of the refugees were not the primary reason of the thorough destruction of numerous Turkish villages and towns in the Gemlik-Yalova Peninsula.

[21] Turkish irregulars responded by attacking Christian villages in the Iznik region, east of Yalova and outside the area controlled by the Greek forces.

[15] The documents in the Ottoman archives accuse the Christian emigres of committing the same atrocities and this is agreed by the western allied report.

According to Ottoman archive documents, the villages of Dutluca (7 September 1920), Bayırköy and Paşayayla in the region of Orhangazi were burned and the population massacred.

The next day there was a massacre in the nearby Turkish village of Çakırlı, men were locked in the local mosque where they were burned alive and shot.

[1] Finally in May 1921, an Inter-Allied commission, consisting of British, French, American and Italian officers,[a] and the representative of the Geneva International Red Cross, Maurice Gehri, was set up to investigate the situation.

[4] The commission listened to various cases; including the rape and torture of a sixty years old women by six Greek soldiers.

[15] To protect the Muslims of further atrocities, the allied commission decided to transport refugees with boats to Istanbul.

[15] But Greek officers insisted on retaining the able bodied men guaranteeing proper treatment, the commission accepted.

[3] The Inter-Allied commission, consisting of British, French, American and Italian officers,[a] and the representative of the Geneva International Red Cross, Maurice Gehri, prepared two separate collaborative reports on their investigations in the Yalova-Gemlik Peninsula.

[25] And the commissioners mentioned the "burning and looting of Turkish villages", the "explosion of violence of Greeks and Armenians against the Turks", and "a systematic plan of destruction and extinction of the Moslem population".

– Maurice GehriThe later famous historian Arnold J. Toynbee was active in the area as a war reporter, Toynbee stated that he and his wife were witnesses to the atrocities perpetrated by Greeks in the Yalova, Gemlik, and İzmit areas and they not only obtained abundant material evidence in the shape of "burnt and plundered houses, recent corpses, and terror stricken survivors" but also witnessed robbery by Greek civilians and arsons by Greek soldiers in uniform in the act of perpetration.