Saudi Arabia and the United Arab Emirates (UAE), which came together against the Iran-backed Houthis in war-torn Yemen, are now experiencing their biggest rift in decades. The UAE backs the separatist Southern Transitional Council (STC) that seized swathes of southern Yemen from the internationally recognised government last month.Saudi Arabia, which backs the internationally recognised government, regarded that move as a threat. On December 30, it bombed Yemen’s port city of Mukalla after a UAE weapons shipment allegedly arrived for the separatist forces. The UAE, in response, said it would withdraw its remaining troops from Yemen. And on Friday, the STC made its intention to secede clear, saying it plans to hold a referendum on independence in two years. The statement came as Saudi-backed forces fought to recapture areas the separatists seized last month.The crisis is escalating by the day. But what are Saudi Arabia and the UAE doing in Yemen in the first place? How did the allies end up on opposite sides? And why has the country been roiled by conflict? Who controls what in Yemen?First, it is important to understand the key players in the conflict in Yemen, where tribal affiliations often dictate loyalties. These are the Iran-backed Houthis in the north, the Saudi-backed President Leadership Council (PLC), also in the north, and the UAE-backed Southern Transitional Council (STC) in the south. A map of Yemen, posted on X by APCurrently, the Houthis control the national capital, Sana’a, along with most of the northern and western parts of the country. The Houthi fighters, over the years, have seized control over areas including Saada, Hajjah, and Al Hudaydah. Story continues below this adThe Saudi-backed PLC, which is recognised internationally, governs areas such as Marib, Hadramawt and Al Mahrah. Its influence in the area is receding as STC fighters move north.In the south, the UAE-backed STC controls Aden, Lahj and parts of Abyan, pushing for autonomy in the region. Meanwhile, Al Qaeda in the Arabian Peninsula and other militant groups maintain a presence in the remote areas of Abyan and Shabwah. These groups have weakened over the years. But with trained fighters, they have the potential to ally with any group from the north and south.A brief history of the conflict in YemenIn 2015, a coalition of Gulf states led by Saudi Arabia, including the UAE, Kuwait, Bahrain and Qatar, came together to quell the Iran-backed armed Houthi group that was leading a popular Arab Spring-like movement in Yemen.Story continues below this adWhile the Saudis offered its Air Force to strike the key Houthi-controlled areas, UAE troops led the ground operations. The two states, working in tandem, even sidelined Qatar, accusing it of supporting “terrorists”.In 2019, the UAE decided to scale down its troop presence in Yemen, but continued to support the STC. The STC, formed in 2017, seeks autonomy or independence of South Yemen in the form it existed before Yemen’s unification in 1990. South Yemen, or the People’s Democratic Republic of Yemen, was the only Communist Arab state. It agreed to unification with the northern Yemen Arab Republic after a civil war in 1986 ended its political leadership. After unification, the north dominated and the main southern party tried to secede, leading to a brief war in 1994 that was quickly won by the northern government based in Sana’a.Story continues below this adThe STC is a dominant force in Aden and other southern governorates and often clashes with the Saudi-backed forces and the PLC. This frame grab from video broadcast by Saudi state television on Tuesday, Dec. 30, 2025, shows what the kingdom describes as a shipment of weapons and armored vehicles coming from the United Arab Emirates, at Mukalla, Yemen. (Saudi state television via AP)In December, the STC made rapid advances in southern and eastern parts of the country and took control of areas in Hadramout and Al Mehrab. These areas have rich oil resources and are close to Saudi territory. The Saudis have flagged the UAE-backed STC’s advancement as a threat to its security and have accused the UAE of aiding its enemy rather than fighting the Houthis. Moreover, the STC’s access to the Red Sea and the Bab el Mandeb Strait — crucial to global shipping — has made the Saudis even more nervous. So why are Saudi Arabia and the UAE backing different parties in the conflict?Story continues below this adThe cracks in the Saudi-UAE coalition started to appear in 2019 when the UAE decided to withdraw its troops from Yemen while continuing its support for STC. While the Saudis wanted the PLC to run the country and ensure its security and interests in the region, UAE’s arms supplies to the STC made reconciliation more difficult.While the two monarchies understand the challenges in the war-torn Yemen, they have spelt out their respective gameplans. The Saudi monarchy is backing the internationally recognised PLC, led by its chairman Rashid al-Alimi. This is because it is in the Saudi interest that a globally accepted leader, who prioritises Saudi security, rule the country. The UAE, on the other hand, despite deciding to pull out troops from south Yemen has, so far, not made any statement about its support for the STC, something that is keeping the Saudi security experts on their toes.Story continues below this adMeanwhile, the Iran-backed Houthi rebels remain the biggest challenge for both Gulf powerhouses. The Houthis, during the conflict with the Saudis as well as with Israel, have shown their ability to withstand military strikes. They remain the most powerful and popular group in the country. They have remained quiet while the Saudi and UAE-backed groups attacked each other. Both Saudi Arabia and UAE must have a plan for the Houthis, but for now, the former allies face the prospect of reconciling their competing political visions.