In the two weeks since the US and Israeli strikes on Iran began, Donald Trump’s war aims have fluctuated between crippling Iranian military capabilities and toppling the regime that has ruled there since 1979. But despite the success of the initial strikes, which killed the supreme leader, Ali Khamenei, many analysts believe that air power alone will not be sufficient to bring about regime change.They say this objective would be impossible to achieve without combat troops on the ground, a move that most US military and political leaders have long opposed. Instead, one idea that seems to be circulating in Washington is to support an invasion by armed Kurdish groups in Iraq and western Iran to destabilise the Islamic Republic from within. Trump publicly backed away from this idea on March 6, telling reporters: “I don’t want the Kurds to go into Iran … The war is complicated enough as it is.” But, given Trump’s trademark inconsistency and the unpredictable nature of this conflict, an armed Kurdish uprising remains a distinct possibility. Such a scenario could have consequences that extend far beyond Iran.The Kurds are an ethnic group with their own language and culture who have lived in a mountainous area of the Middle East for centuries. Nowadays, they number around 30 million and live in a region that spans parts of Turkey, Iran, Iraq and Syria. The Kurds are widely considered to be the world’s largest stateless people because they do not have a country of their own.This situation dates to the end of the first world war, when the Ottoman empire collapsed. Kurdish leaders at that time hoped to establish their own state, having lived for 400 years under Ottoman rule. But instead their homeland was divided between several new countries that emerged from the defeated Ottoman state. This left Kurdish communities split across internationalAround 10% of Iran’s population is Kurdish and many live in the country’s north-west near the borders of Iraq and Turkey. The Kurdish region of Iran has long been the least economically developed part of the country and Kurdish political parties are outlawed. Armed Kurdish groups have periodically clashed with the Iranian state, demanding greater autonomy or independence.The Kurdish question is even more sensitive in Turkey, which is home to the largest population of Kurds in the world. Since 1984, the Turkish state has been locked in conflict with the Kurdistan Workers’ party (PKK), an armed group that has fought to establish an independent Kurdish state. This conflict has killed more than 40,000 people in the past four decades.For the Turkish government, the possibility that the US may support Kurdish fighters in neighbouring Iran is therefore not just a foreign policy issue. Turkish leaders worry that strengthening Kurdish armed groups elsewhere in the region could embolden similar movements inside Turkey itself.In the recent past, Turkey has launched military incursions into the Kurdish regions of Iraq and Syria. It has also fought a brutal counterinsurgency against PKK fighters inside its own borders. These actions show how strongly Turkish leaders oppose any notion of Kurdish independence anywhere in the region.American support for Kurdish fighters has caused tension between the US and Turkey in the past. Turkey strongly opposed the partnership between Washington and Syrian Kurdish forces during the fight against the Islamic State militant group in Syria in the late 2010s. It argued that some of these Kurdish groups were linked to the PKK.Turkey’s relations with Israel have also been strained by the Kurdish question. The Turkish president, Recep Tayyip Erdoğan, has accused the Israeli prime minister, Benjamin Netanyahu, of undermining the transitional Syrian government by aiding Kurdish groups there. The Kurdish issue has clearly become a major source of tension between Turkey, a key member of the Nato alliance, and the west.So far, Turkey has largely remained neutral in the Iran war. Despite their regional rivalry, Turkish and Iranian leaders share concerns about Kurdish separatist movements and have sometimes cooperated to contain them. In the past, security forces from both countries have coordinated efforts against Kurdish militant groups operating along their shared border. Turkish and Iranian officials have also exchanged intelligence and carried out military operations against Kurdish fighters moving between the two countries. And both governments strongly opposed the 2017 referendum on independence that was held by the Kurds in northern Iraq. Over 92% of votes were cast in favour of independence. Iranian regime changeFor Turkey, the collapse or fragmentation of the Iranian state would be deeply worrying. It could create exactly the conditions Turkish leaders fear most: armed Kurdish groups operating across a much longer and more unstable border.Another concern is the possibility of a new refugee crisis.