The Kurds - whose representatives on Thursday declared a unified, federal region in northern Syria that was objected to by the state's regime, opposition and the US - number an estimated 25-35 million people in four countries.
The Kurds inhabit mainly mountainous regions that cover almost half a million square kilometers (200,000 square miles), spanning from southeast Turkey through northern Syria and Iraq to central Iran.
They number around 12-15 million in Turkey, (about 20% of the overall population), five million in Iran (less than 10%), 4.6 million in Iraq (15-20%), and about three million in Syria (15%).
Kurds have preserved their culture, dialects and clan-based social structures, and large expatriate communities exist in Armenia, Azerbaijan, Germany and Lebanon.
Tense relations with host countries
Kurdish ambitions of a unified nation are seen as a threat to the main host countries.
- In Turkey, the outlawed Kurdistan Workers' Party (PKK) has been labeled a terrorist organization by the European Union and the United States. Over 30 years of fighting with Turkish forces has killed more than 45,000 people.
Ankara blames the PKK for a car bombing in the city that killed 35 people on Sunday, and has since bombed PKK camps in northern Iraq.
- In Syria, the US-backed Kurdish People's Protection Units (YPG) are one of the most effective forces against the Islamic State (ISIS) jihadist group.
They control more than 10% of the country in the north and northeast, and three-quarters of the border with Turkey.
- In Iraq, Kurds are an important US ally, and after resisting the army of Saddam Hussein for decades, now lead the fight against ISIS.
They control roughly 40,600 square kilometers (15,600 square miles) of territory, including many of northern Iraq's oil fields and the cities of Arbil and Kirkuk.
- In Iran, where the army crushed a fledgling Kurdish republic in 1946, the Party for Free Life in Kurdistan (JAK) is pushing for autonomy in three provinces.
Kurdish peshmerga fighters are considered experienced warriors and Western countries have provided them with air cover, sophisticated weapons and training to combat ISIS jihadists trying to establish a "caliphate" that would include Kurdish lands in Iraq and Syria.
Although predominantly Sunni Muslims, some Kurds are Christians and their political structures are often non-denominational.
Notable Kurdish victories include the YPG's four-month assault of ISIS fighters in Kobane on Syria's border with Turkey and peshmerga gains in Iraq.
Turkey has regularly attacked YPG positions in Syria since mid-2015.
AFP contributed to this report.