Iraqi Kurds last month backed independence from Baghdad in a controversial referendum that has heightened regional tensions.

Indigenous to a mountain region in the northern Middle East, the Kurds are the largest stateless nation in the world. The fourth largest ethnic group in the Middle East, around 25 million Kurds live in a territory that spans the borders of modern-day Turkey, Iraq, Syria, Iran and Armenia.

Kurds have a distinct community, united by race, culture and language - although several dialects exist. Due to the cross-border nature of their nation since the collapse of the Ottoman Empire, Arabic and Turkish are also widely spoken.

They have a long history of political marginalisation and persecution, and have repeatedly risen up, particularly in Iraq and Turkey, in pursuit of greater autonomy or complete independence.

The destabilisation of Iraq, the war in Syria, and the rise of the self-proclaimed Islamic State of Iraq and the Levant (ISIL, also known as ISIS) have presented new challenges for the Kurds, as Kurdish forces have played an increasingly important role in the battle against ISIL.

Did you know? The Kurds are one of the largest stateless populations in the world.

The Kurdish population is similar to that of Canada and Australia.

Kurdish women lead the world in female fighters, accounting for 40 percent of the military.

The Kurdish Regional Government has more women than both the United States and the United Kingdom, with 30 percent of seats in the government reserved for women.

Iraq's Kurdish region spends at least 16 percent of its annual budget on education, more than the US and Canada.

One in four people living in Iraq's Kurdish region is a refugee or an internally displaced person. Source: The Kurdish Project

Historical background

At the end of World War I, the Treaty of Sevres was drafted to deal with the dissolution and partition of the Ottoman Empire.

The treaty bolstered Kurdish national aspirations by providing for a referendum to decide the issue of the Kurdish homeland.

The Treaty of Sevres was rejected by the new Turkish Republic, and a new treaty (the Treaty of Lausanne) was negotiated and signed in 1923.

The Treaty of Lausanne gave control of the entire Anatolian peninsula, or Asia Minor, to the new Turkish Republic, including the Kurdish homeland in Turkey.

There was no provision in the new treaty for a referendum for Kurdish independence or autonomy. Kurdish hopes for an autonomous region and independent state were dashed for the next few decades.

From the end of World War I to the Gulf War in 1990, the Kurds in Turkey, Iran, Iraq and Syria fought separate campaigns to achieve autonomy.

All of the campaigns were forcibly put down and the Kurdish people suffered greater suppression each time.

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Who are the Kurds in Iraq?

After decades of military and political struggle, Kurds in Iraq secured constitutional recognition in 2005 of an autonomous Kurdish region in the north of the country.

Prior to 2005, the Kurds of Iraq launched successive rebellions aimed first at the British and later at the government in Baghdad.

Successive Iraqi administrations, particularly starting in the late 1970s, forcibly displaced hundreds of thousands of Kurds from northern Iraq, through a policy known as "Arabisation", and repopulated the areas with Arabs from central and southern Iraq.

The scale of the displacement of Kurds in the north during the mid-1970s was immense, displacing the entire Kurdish population from an area reaching from the town of Khanaqin, close to the Iranian border, to the Syrian and Turkish border areas around Sinjar.

In the 1980s, Saddam Hussein's government destroyed at least 4,000 villages and forcibly moved their residents to collective towns. In 1988, Hussein unleashed a campaign of vengeance on the Kurds that included a poison-gas attack on Halabja.

The Iraqi High Criminal Court later charged Hussein with genocide for attempting to annihilate the country's Kurds through military operations in 1988 that killed at least 50,000 civilians and destroyed thousands of homes.

The first glimpse of autonomy came in 1991, during the first Gulf War, when the US-led coalition fighting Hussein established a partial no-fly zone in northern Iraq. The stability allowed Kurdish forces to steadily gain control of the territory and paved the way for the 2005 constitutional agreement.

And while Iraq's autonomous Kurdish areas, also known as Iraqi Kurdistan, largely escaped the chaos and destruction that existed in the lead-up to and after Hussein's removal in 2003, major tensions remain.

The Kurdish Regional Government (KRG) has not yet defined its boundaries. Many Kurds are hoping to expand the current borders to include "contested" areas, many of which were Arabised under Hussein, including the Kurdish-majority city of Kirkuk - an oil-rich province the Kurds consider their "Jerusalem".

In the summer of 2014, as ISIL forces swept across large swaths of Iraq, Kurdish Peshmerga forces pre-emptively moved into the city to prevent it from falling into the group's hands.

Tensions also exist between the two main political parties, the Patriotic Union Party (PUK) and the Kurdistan Democratic Party (KDP), who fought a civil war from 1994 to 1997.

KRG President Massoud Barzani (KDP) announced in July 2014 that his government planned to hold a referendum on independence from Iraq. The declaration caused alarm in neighbouring countries, who were fearful that their own restive Kurdish populations would follow suit.

Results of the September 25 referendum showed that a majority of Iraqi Kurds supported secession.

After the Gulf War

After the 1990-1991 Gulf War and the no-fly zone enforced by the United States in Iraq's Kurdish region, Iraqi Kurds had autonomy.

In 1992, an alliance of political parties, the Iraqi Kurdistan Front, held parliamentary and presidential elections.

As a result, the Iraqi Kurdistan Front established the KRG, an autonomous government for Iraq's Kurdish region.

Today, at least 5.2 million people live in Iraq's Kurdish region, according to the KRG.

They have their own parliament, military (the Peshmerga), borders and foreign policy.

In 1994, a power-sharing arrangement between the PUK and the KDP collapsed.

In 2003, the US invaded Iraq and the Peshmerga joined in the fight to overthrow Hussein.

After Hussein was driven from office, the Iraqis, in a national referendum, approved a new constitution. The new constitution recognised the KRG and the Kurdish parliament.

In 2006, the PUK and KDP arranged to unify administrations under Prime Minister Nechirvan Barzani.

Kurds remain dependent on their neighbours for access to markets and to export oil, the Kurds' main economic resource.

Kurds in Turkey

Half of the Kurdish nation resides in Turkey, where they make up about 20 percent of the local population.

Modern Turkey's constitution denies the existence of distinct ethnic sub-groups, and since the country's founding, any expression by Kurds or other minorities of their unique ethnic identity has been repressed. The Kurdish language, spoken by millions in Turkey, was outlawed until 1991.

Ankara has consistently shut down Kurdish attempts to politically organise, and any action that hints at Kurdish nationalism is considered an offence punishable by imprisonment. The Turkish government has also been accused of systematically withholding resources from the country's Kurdish areas.

Abdullah Ocalan established the Kurdistan Workers' Party (PKK) in 1978, calling for an independent state inside Turkey.

In 1984, the PKK launched an armed struggle against the Turkish state, which eventually left between 30,000 and 40,000 people dead and hundreds of thousands displaced, according to the International Crisis Group.

The PKK launched attacks against government property, government officials, Turks living in Kurdish areas and Kurds it accused of collaborating with the government.

In 2012, the Turkish government and the PKK began peace talks, and in 2013 a ceasefire was agreed on, although clashes continued.

In July 2015, the ceasefire collapsed a few days after a suicide bombing blamed on ISIL killed at least 33 young activists in the mainly Kurdish town of Suruc, near the Syrian border.

The United Nations said in a report this year that at least 2,000 people, including 1,200 local residents and 800 members of the security forces, have been killed in the latest wave of violence.

The PKK has attacked Turkish soldiers and police, while the Turkish government has launched what it called a "synchronised war on terror" against the PKK and ISIL.

Since then, air strikes on PKK camps in northern Iraq and clashes have killed hundreds of people.

What is the situation in Syria?

In Syria, the Democratic Union Party (PYD) is one of the most prominent Kurdish opposition parties. It comprises a major part of the Syrian Democratic Forces (SDF), an alliance of Kurdish, Arab, Assyrians, Armenian, and Turkmen groups that was established in October 2015.

The PYD was founded in 2003 as an offshoot of the PKK, to which it remains closely tied. The PYD's armed wing is the People's Protection Units (YPG). The group has coordinated with both Syrian rebels and government forces in different parts of Syria to further its interests.

During the Syrian conflict, it managed to carve out a mini-state in three provinces in the country's north - Aleppo, Raqqa and Hassakah.

Backed by US coalition air strikes, the US-backed SDF have been fighting ISIL in an effort to recapture Raqqa, the armed group's self-declared capital.