The schism between Sunnis and Shiites in Islam has divided the Middle East for several centuries. Here's a look at how the old religious divide has translated into a modern war in Yemen.
In September 2014, Houthi rebels took over the Yemeni capital of Sanaa, declaring President Abed Rabbo Mansour Hadi's government invalid and unleashing a flurry of events that peaked in a civil war in March 2015.
While President Hadi fled Sanaa to the southwestern city of Aden and then to Saudi Arabia, the neighboring kingdom's military and coalition, with the assistance of the United States, launched ground operations and airstrikes against Houthi rebels and former president Ali Abdullah Saleh's supporters in Yemen.
Since then, at least 10,000 people have been killed in the country. A report by the UN Office for the Coordination of Humanitarian Affairs earlier this year said at least 14.4 million Yemenis were unable to meet their food needs, with more than half of them facing severe food insecurity. Over 19 million lacked access to clean water and sanitation and around 2 million were displaced within or outside the country.
Historically, Shiites, also known as Shias, favored the election of Prophet Mohammed's cousin and son-in-law Ali ibn Abi Talib to take the Prophet's place after his death in 632. Sunnis, on the other hand, elected Abu Bakr, the Prophet's companion, as the first caliph or leader of the Islamic community. "The two countries that compete for the leadership of Islam, Sunni Saudi Arabia and Shia Iran, have used the sectarian divide to further their ambitions," CFR said.
Saudi Arabia's interest in Yemen began in the early 1920s with attempts to control Yemen's myriad tribes and secure its outer borders, Nachum Shilo, research fellow at Tel Aviv University's Moshe Dayan Center for Middle East and African Studies told DW. Another crucial reason why the kingdom was interested in Yemen was Sanaa's access to the Bab el-Mandeb strait, which connects the Red Sea to the Indian Ocean and is Saudi Arabia's main gateway for exporting oil, he added.
The current intervention
"Saudi Arabia built the Arab coalition to intervene in Yemen in order to prevent something from happening, rather than to make something happen. And that is to prevent Yemen from becoming another Iraq, where sovereignty lies in Tehran, not in Baghdad," according to Mansour Almarzoqi, researcher on Saudi Arabian affairs at the Sciences Po in Paris.
In the article published by the Carnegie Endowment for International Peace, Almarzoqi suggests that intervening in Yemen helps Saudi Arabia stave off Iran, whose interventionist and expansionist policies involve arming Syrian President Bashar al-Assad's supporters and building militias in Iraq to increase its sphere of influence.
"So the best outcome of the Yemeni crisis for the Saudi-led Arab coalition is to see the Iranian-backed Houthi militia and Saleh forces withdrawing from state institutions, ending their siege of cities like Taiz, turning in heavy weapons (including ballistic missiles), and agreeing to the formation of a unity government whose composition reflects all components of Yemeni society," Almarzoqi suggests.
Why have peace talks failed?
Meanwhile, the war continues. The Saudi-led coalition has carried out several airborne attacks on civilian targets, including hospitals run by international aid groups in the last months.
In August this year, Houthi rebels rejected a deal brokered by the United Nations, which proposed that rebels hand over the capital Sanaa and other cities they were controlling. They would also have to surrender heavy weapons to a military committee formed by President Mansour Hadi and free prisoners of war.
The rebels' demand for a new parliament and president was rejected.
Peace remains elusive
On Saturday, warplanes from the Saudi-led coalition bombed a funeral procession, killing 140 people, including prominent Houthi rebel leaders. There were protests following the attack, including condemnation by the US, which has been offering military support to Riyadh in the strikes. The international community has also called for a probe into human rights violations in the country.
"Yemen has too many players and too many tribes who can't be controlled," Tel Aviv researcher Nachum Shilo told DW. These tribes have never had to listen to a central government in their history, he said, adding that in this situation, "a ceasefire is doomed."