Everything you need to know about conflict that has turned country into humanitarian catastrophe

How long has the war been going on?

Yemen has been troubled by civil wars for decades, but the current conflict intensified in March 2015 when a Saudi-led coalition intervened on behalf of the internationally recognised government against Houthi rebels aligned with the former president Ali Abdullah Saleh.

The war is widely regarded as having turned a poor country into a humanitarian catastrophe. Riyadh expected its air power, backed by regional coalition including the United Arab Emirates, could defeat the Houthi insurgency in a matter of months.

Instead some reports suggest nearly 100,000 people have died. Others put the death toll much lower, but fighting this year alone has displaced 250,000 people. There are more than 30 active front lines. A total of 80% of the population – more than 24 million people – need assistance and protection, including 10 million who rely on food aid to survive.

What is the cause of the war?

Its roots lie in the Arab spring. Pro-democracy protesters took to the streets in a bid to force the president, Ali Abdullah Saleh, to end his 33-year rule. He responded with economic concessions but refused to resign.

By March 2011, tensions on the streets of the capital city, Sana’a, resulted in protesters dying at the hands of the military.

Following an internationally brokered deal, there was a transfer of power in November to the vice-president, Abd Rabbu Mansour Hadi, paving the way for elections in February 2012 – in which he was the only candidate to lead a transitional government. Hadi’s attempts at constitutional and budget reforms were rejected by Houthi rebels from the north.

The Houthis belong to a small branch of Shia Muslims known as Zaydis. They captured the capital, forcing Hadi to flee eventually to Riyadh. There is also a strong secessionist movement in the south. Arguably too many sides benefit financially from the status quo.

Is Britain backing the Saudi-led coalition?

The British play a dual role as diplomatic penholders on the Yemen file at the UN security council and military advisers to the Saudi coalition in Riyadh. Critics, including some Tory MPs, say this places the UK in the invidious role of broker and belligerent.

UK diplomats, including some Saudi sceptics, claim it has influence over not just Saudi military strategy but also its diplomatic thinking, restraining the Saudis for instance from launching an all out assault on the port city of Hodeidah. It has always claimed the sale of arms to Saudis is justified in part because it buys influence with its security partner in the Gulf.

What has happened to the peace process?

The UN brokered an agreement in Stockholm in December to demilitarise the Red Sea city of Hodeidah, and after five months of tortuous talks a small part of the agreement has been implemented on the ground. The Houthis had promised a two-phase redeployment out of the city, and agreed that an alternative force – poorly defined in the Stockholm agreement – would take over security in the areas they vacated. But talks between the Houthis and the UAE-backed government forces stalled over the details.

Faced by an impasse, the UN sanctioned a unilateral Houthi withdrawal from the three main ports on Yemen’s Red Sea coast – Hodeidah, Ras Issa and Saleef. The Yemeni government described the withdrawal as a sham, saying the Houthis had merely rebadged their fighters as coastguards. They pressed for the resignation of Martin Griffiths, the UN special envoy for Yemen. Not everyone in the Yemen government agreed with this analysis and the foreign minister quit.

No progress has been made on the second phase of redeployment, or the exchange of political prisoners. Griffiths is now trying to secure enough progress in Hodeidah to get off this hook and say the time is ripe for wider political talks on a transitional government to be held in Bonn.

Is Yemen becoming connected with the wider Gulf tensions?

Yes. The Houthis, with a disputed degree of assistance from Iran, have stepped up their use of drone and missile strikes into bordering Saudi Arabia. In turn the UAE and Saudi claim these attacks are being orchestrated by Tehran to put pressure on Saudi, America’s chief ally, in the drive to make Iran renegotiate the nuclear deal, and end its regional interference.

The Houthis claim the drone strikes are justified retaliation for the repeated Saudi airstrikes.