The massacre began with ISIL attacking and capturing Sinjar and neighboring towns on 3 August, during its Northern Iraq offensive.

After Iraqi federal military forces fled from the advancing ISIL troops, local residents seized their abandoned weapons in case of an attack by the Islamic State.

[3] There is general agreement that the majority of the forces in Shingal on that day were affiliated with the KDP, despite wildly varying estimates as to troop levels.

[30] ISIL then detonated the Sayyidah Zaynab Mosque in Sinjar, executed resisters, and demanded the residents swear allegiance and convert to Islam or be killed.

[13][31] About 50,000 Yazidis fled into the Sinjar Mountains,[31] where they were trapped without food, water or medical care[32] and faced starvation and dehydration.

[31] The U.S. government, Kurdish Peshmerga forces, and Western media reported that thousands of Yazidis in the Sinjar Mountains were under siege by ISIL.

[33][34][35][36][37] Tahseen Said, the emir of the Yazidis, issued an appeal to world leaders on 3 August 2014, asking for humanitarian help to aid those who were besieged by ISIL.

[32] On 7 August 2014, The New York Times reported that ISIL had executed dozens of Yazidi men in Sinjar city and had taken their wives for forced marriage.

[39] It was also reported that ISIL fighters executed ten caretakers of the Shia Sayeda Zeinab shrine in Sinjar before blowing it up.

250–300 men were killed in the village of Hardan, 200 between Adnaniya and Jazeera, 70–90 in Qiniyeh, and on the road out of al-Shimal witnesses reported seeing dozens of bodies.

[14] Kurdistan Region estimated in December 2014 that the total number of killed or missing Yazidi men, women and children from Sinjar since August amounted to around 4,000.

[49] On 12 August, an Iraqi military helicopter, piloted by Maj. Gen. Majid Abdul Salam Ashour, crashed in the mountains while delivering aid and rescuing stranded Yazidi refugees.

[16] On 13 August, a 16-aircraft mission including US C-17s and C-130Hs, an Australian C-130J, and a British C-130J delivered supplies to mostly Yezidi civilians stranded on Mount Sinjar.

[54] On 7 August 2014, the U.S. President, Barack Obama, stated that the U.S. was starting air strikes to prevent a potential massacre (genocide) by ISIL of thousands of Yazidis trapped in the Sinjar Mountains.

And we strive to stay true to the fundamental values – the desire to live with basic freedom and dignity – that is common to human beings wherever they are.

[60] On 12[33] or 13 August 2014, a dozen U.S. Marines and special forces servicemen landed on Mount Sinjar from CH-53E aircraft to assess options for a potential rescue of Yazidi refugees joining British SAS already in the area.

This was reportedly done by U.S airstrikes and Kurdish fighters of the People's Protection Units from Syria, together with their PKK allies from Turkey,[1][3] allowing more than 50,000 refugees to escape.

ET, the US carried out five additional airstrikes on armed vehicles and a mortar position, enabling 20,000–30,000 Yazidi Iraqis to flee into Syria and later be rescued by Kurdish forces.

[71] In a statement on 14 August 2014, The Pentagon said that the 20 US personnel who had visited the previous day had concluded that a rescue operation was probably unnecessary since there was less danger from exposure or dehydration and the Yazidis were no longer believed to be at risk of attack from ISIL.

[72][73][74] Kurdish officials and Yazidi refugees stated that thousands of young, elderly, and disabled individuals on the mountain were still vulnerable, with the governor of Kurdistan's Dahuk province, Farhad Atruchi, saying that the assessment was "not correct" and that although people were suffering, "the international community is not moving".

After ISIL forces retreated, Kurdish fighters were initially faced with clearing out mines in the area,[84] but quickly opened a land corridor that enabled Yazidis to be evacuated.

[65] Late on 21 December 2014, Syrian Kurdish YPG fighters south of the mountain range reached Peshmerga lines, thus linking their two fronts.

[88][89] In March 2019, the first mass grave site in Sinjar was exhumed by the Iraqi Mass Graves Directorate within the Martyr's Foundation and the Medical Legal Directorate under the Iraqi Ministry of Health in conjunction with UNITAD (United Nations Investigative Team to Promote Accountability for Crimes Committed by Da’esh/ISIL).