Sunni Triangle in the context of "Ramadi"

Samarra (Arabic: سَامَرَّاء, Sāmarrāʾ) is a city in Iraq. It stands on the east bank of the Tigris in the Saladin Governorate, 125 kilometers (78 mi) north of Baghdad. The modern city of Samarra was founded in 836 by the Abbasid caliph al-Mu'tasim as a new administrative capital and military base. In 2003 the city had an estimated population of 348,700. During the Iraqi Civil War (2006–08), Samarra was in the "Sunni Triangle" of resistance.

The archeological site of Samarra still retains much of the historic city's original plan, architecture and artistic relics. In 2007, UNESCO designated it a World Heritage Site.

Fallujah (Arabic: ٱلْفَلُّوجَة al-Fallūjah [el.fɐl.ˈluː.dʒɐ]) is a city in Al Anbar Governorate, Iraq. Situated on the Euphrates River, it is located roughly 69 kilometres (43 mi) to the west of the capital city of Baghdad and 50 kilometres (31 mi) from the neighboring city of Ramadi. The city is located in the region defined as Sunni Triangle by the United States, as the majority of its residents are Sunni Arabs. In 1947, Fallujah was a small town with a relatively small population but had grown to a population of about 250,900 people by 2018.

Following the 2003 invasion of Iraq, which triggered the Iraq War, the city became a major centre of resistance during insurgency. The United States, the United Kingdom, and the Iraqi Interim Government twice engaged in fierce urban combat with insurgents throughout the city; the first battle of Fallujah failed to dislodge the insurgents, triggering the second battle, in which the coalition forces successfully took control of the city. However, heavy fighting from these two battles left the city severely damaged, though it remained occupied by the coalition until 2011. In January 2014, three years after the American withdrawal from Iraq, Fallujah was captured by the Islamic State (IS) and suffered a major population decline. On 23 May 2016, the government announced the beginning of a large-scale military offensive against the IS militants occupying the city, resulting in the Third Battle of Fallujah. On 26 June 2016, the Iraqi Armed Forces stated that Fallujah had been fully liberated and was free from militant control.

The Saladin, Salah ad Din, or Salah Al-Din Governorate (Arabic: محافظة صلاح الدين, Muḥāfaẓat Ṣalāḥ al-Dīn) is one of Iraq's 19 governorates, north of Baghdad. It has an area of 24,363 square kilometres (9,407 sq mi), with an estimated population of 1,042,200 people in 2003. It is made up of 8 districts, with the capital being Tikrit. Before 1976 the governorate was part of Baghdad Governorate.

The governorate is named after Saladin or Salah ad-Din. This governorate is largely Sunni Arab and is also where Saddam Hussein, former president of Iraq, was born, in the village of Al-Awja. Salah Al-Din governorate, a traditional stronghold of Saddam and his Al-Bu Nasir tribe that is located in the heart of the Sunni Triangle, has been a centre of insurgencies, tribal rivalries, and political and sectarian violence since the 2003 U.S.-led Coalition invasion of Iraq.

Sunni Islam in Iraq (Arabic: الإسلام السني في العراق) is the second-largest sect of Islam in Iraq after Shia Islam. The majority of Iraqi Sunni Muslims are Arabs with the second largest being Kurds. Iraqi Sunni Muslims mainly inhabit the western and northern half of Iraq. Sunni Arabs primarily inhabit the Sunni Triangle, Upper Mesopotamia and the desert areas, such as Al-Anbar Governorate in the Arabian Desert and Syrian Desert. The Sunni Kurds inhabit the mountainous Iraqi Kurdistan region.

In 2003, the United States-based Institute of Peace estimated that around 95% of the total population of Iraq were Muslim, of which Sunnis made up around 40%. A CIA World Factbook report from 2015 estimates that 29–34% of the population of Iraq is Sunni Muslim. According to a 2011 survey by Pew Research, 42% of Iraqi Muslims are Sunni. There were about 9 million Sunni Arabs, 4 million Sunni Kurds and approximately 1.5 million Sunni Turkmens in Iraq (approximately 39%), according to a report published in 2015.