The rebel forces did not put up any significant opposition to the clearing operation, and either retreated into nearby Montenegro, or hid their weapons in the mountains and went home.

[7] The Italians handed over the administration of eastern Herzegovina to the NDH government on 20 May 1941, following the signing of the Treaties of Rome, which ceded formerly Yugoslav territory along the Adriatic coast to Italy.

On 28 May, a group of ten young Ustaše students from the University of Zagreb arrived in Trebinje and began removing signs written in the Cyrillic script used by Serbs.

[15] On that day, the Ustaše students in Trebinje shot nine Serbs and arrested another fifteen, apparently due to their links to the inter-war Chetnik Association.

[16] On the night of 4/5 June, a group under the control of the Ustaše commissioner for the Gacko district, Herman Tonogal,[d] killed 140 Serbs in the village of Korita, near Bileća, and threw their bodies into a nearby sinkhole.

[21] In the immediate aftermath, Serbs and Montenegrins from the local area attacked villages, and Adriatic Command sent the 2nd Company of the 7th Battalion from Bileća to reinforce the Ustaše.

Due to its exposure to fire from rebels overlooking their location, the gendarmes were unable to re-occupy their post in Stepen, which meant that the Stepen–Korita road was no longer secure.

On 8 June, the district office in Gacko reported to Adriatic Command that they had taken 200 Serbs as hostages and issued a proclamation to the population to cease fighting and surrender their weapons.

[23] On 17 and 18 June, Tonogal and Lieutenant Colonel Aganović, gendarmerie commander for eastern Herzegovina, made an attempt to calm the situation by visiting villages east of the Gacko–Avtovac road to re-establish peace in the area.

The gendarmerie commander in Bileća believed that the reason for the rebellion was that the local Serbs were wedded to the idea of Greater Serbia, and did not accept that their villages were part of the NDH.

[25] The response of the NDH authorities to resistance had been to burn down the villages where this had occurred, and there were mass shootings of Serbs, which escalated the level of violence even further.

[26] The NDH authorities only had weak forces in eastern Herzegovina at the time the mass uprising occurred, roughly equal to two Croatian Home Guard battalions, as well as gendarmerie posts in some towns.

Over the period 23–25 June, 150 Serbs from the village of Ravno, 30 km (19 mi) southwest of Ljubinje, were arrested and killed at the gendarmerie post, and the remainder of the population fled to the hills.

Professor Marko Attila Hoare states that the full-scale uprising resulted from the Ustaše retaliation against attempts of the Serbs of eastern Herzegovina to defend themselves, combined with the launching of the German invasion on 22 June.

That morning, reports also arrived from Bileća and Stolac that rebels were approaching the village of Berkovići from the north, and had captured the gendarmerie post at Gornji Lukavac.

[33] In the southern part of the area of operations around Stolac, the situation was significantly calmer than around Nevesinje, although a group of 200 Ustaše at Berkovići were falsely claiming that they were being surrounded by rebels at night.

Their attack commenced about 10:00, and although they faced strong resistance from the rebels, aided by strafing and bombing by ZNDH aircraft, they reached villages on the outskirts of Nevesinje after fighting that lasted until dawn on 28 June.

Army Chief of Staff General Vladimir Laxa was immediately appointed by Pavelić to control both Hum and Dubrava counties, which incorporated much of eastern Herzegovina.

[38] On 28 June, Laxa became the overall commander of all NDH authorities in Hum and Dubrava counties, which included Ustaše, Home Guard, civil administration, gendarmerie and police.

Prohaska had to send reserves to block the road between Nevesinje and Kifino Selo, and the companies from the 11th Battalion began to reconnoitre the rebel positions towards Odžak.

They recovered from their initial surprise and held the town during the day, but in the evening a renewed assault caused them to withdraw from Avtovac and retreat to the villages of Međuljići and Ključ.

[42] There was no improvement in the situation around Stolac, and an Ustaše unit made up of armed civilians proved to be of such low combat value that Laxa spoke to Francetić and criticised its performance.

In the afternoon a platoon of the 10th Home Guard Battalion was sent north from Trebinje to support the gendarmes, but they were attacked near the village of Mosko, and withdrew into a defensive position.

ZNDH aircraft from Mostar airfield flew reconnaissance sorties over the area and dropped leaflets over Stolac, Stepen, Avtovac, Gacko and Plužine.

[46] During the remainder of the day, the Italians collected the bodies of their dead from the rebel ambush on 28 June, and rescued some Home Guard troops that had escaped Avtovac, but then returned to Plana, just north of Bileća.

[48] An Ustaše operation to clear the insurgents from the Stolac district began on 3 July, meeting with success and opening of the road from Berkovci north to Odžak.

Montenegrins involved in the leadership of the uprising included Colonel Bajo Stanišić, Major Minja Višnjić, and Radojica Nikčević from Nikšić.

[50] Following the Italian intervention, Prpić was able to proceed with the task of clearing the wider area of Nevesinje from 3 July, ensuring NDH control of population centres and roads.

[15] Tomasevich states that the uprising was a "spontaneous, unorganised outburst" that was doomed to failure, and involved neither the Chetniks of Draža Mihailović nor the Communist Party of Yugoslavia (Serbo-Croatian Latin: Komunistička partija Jugoslavije, KPJ).

He contends that the uprising was the result of several factors, including the Ustaše persecutions, fear and hatred of the NDH authorities, a local tradition of rebellion against the Ottoman Empire, the poor economic conditions in eastern Herzegovina, and news of the launching of Operation Barbarossa against the Soviet Union.