The United Nations has said a dispute between Yemen’s president and northern rebels has pushed the country to the brink of civil war.
President Abd-Rabbu Mansour Hadi fled Yemen’s rebel-held capital in February, and is seeking to set up a rival power centre in the south with loyalist army units and tribes.
In September 2014, the Houthi rebels seized the capital Sanaa, but agreed to the formation of a unity government after the United Nations brokered peace talks. When they tightened their grip on the capital in January, Hadi and his government resigned, and Hadi was put under house arrest. Hadi later re-claimed the presidency.
Yemen is also experiencing a long-running conflict with southern separatists, and faces a threat from al Qaeda militants, all of which have worsened a major humanitarian crisis.
The government has been fighting southern separatists for many years, and faces a threat from al Qaeda militants, both of which have worsened a major humanitarian crisis.
About 15.9 million Yemenis, out of a population of 25.9 million, need humanitarian aid. Some 10.6 million do not have enough to eat, more than 13 million have no safe water and basic sanitation, the United Nations said in March 2015.
About 840,000 children under five are acutely malnourished, the United Nations said.
Yemen is host to more than 235,000 refugees from Somalia, and some from Ethiopia, Eritrea, Iraq and Syria. Many people die every year trying to make the dangerous journey there by sea from the Horn of Africa.
Yemen is the poorest Arab nation, and its economic hardships are aggravated by a lengthy political crisis as well as conflict on several fronts. It has high levels of unemployment, rapid population growth and diminishing water resources.
It is heavily dependent on dwindling oil supplies, but its oil and gas pipelines have been repeatedly sabotaged by insurgents and tribesmen, causing fuel shortages and slashing export earnings.
Fighting in the northern provinces between the Houthis and the government has raged on and off since 2004, and recently spread south. It has displaced hundreds of thousands of people.
The rebels seized the capital Sanaa in September 2014 after weeks of Houthi-led protests. They imposed informal control of government ministries, and demanded that the government step down and that fuel subsidy cuts imposed in July be reversed. They signed a peace deal with 11 political parties in September, stipulating that a new unity government be formed.
The Houthis then expanded their territory southward and along the Red Sea coast, and took the lead in the fight against al Qaeda militants. They said they were providing security until the government could carry out its responsibilities, according to the International Crisis Group (ICG).
By the end of 2014, they were the dominant authority in nearly half of the country’s 21 governorates, and had representatives in ministries and other state institutions.
The Houthis rejected a draft constitution proposed by the government in January 2015, and seized the presidential palace in Sanaa. The draft was the result of talks between Yemen’s competing factions. The Houthis opposed the draft’s proposal to divide Yemen into six federal regions, and instead supported a plan by southern separatists for just two regions.
WHO ARE THE HOUTHIS?
The Houthis are based in Yemen’s northern highlands and named after the clan of their leader. They are seeking more rights for the Zaydi Shi'ite Muslim sect, a strongly tribal minority in mostly Sunni Muslim Yemen, and want greater autonomy for their heartland of Saada province. They oppose Yemen's close ties with the United States.
Saudi Arabia, Yemen’s largest donor, and some in Yemen consider the Houthis to be proxies of Shi’ite Iran. Tehran has denied supporting them.
Some Yemeni officials say they are getting support from former President Saleh.
Supporters of the Houthi praise their willingness to confront corruption, combat al Qaeda and fill a security vacuum left by the government, says ICG’s April Longley Alley.
In the far north, hundreds of thousands of people have been displaced by fighting in the last few years between the Houthis and government forces.
Fighting escalated in 2009, and the conflict briefly spread to Saudi Arabia where rebels clashed with Saudi forces, accusing the government there of supporting the Yemeni government in attacks against them. The Saudi government denies this.
Despite a shaky ceasefire deal with the government in February 2010, most of the displaced were reluctant to return home because of continued insecurity, a fear of reprisals and a lack of basic services.
The Houthis have clashed with northern followers of Salafism, a puritanical brand of Sunni Islam, and with supporters of the powerful Islamist Islah Party.
Separatists in the south have intensified calls for an independent state for the south, alarmed at the growing chaos in northern Yemen.
The separatists want to revive a southern socialist state that Saleh united with the north in 1990. They initially joined the anti-Saleh protesters in 2011, but the two sides later moved apart.
Yemen's unity was troubled from the start and resulted in a short but bloody civil war in 1994. After that many southerners viewed the north as an occupying force, and their sense of marginalisation by the government eventually resulted in a popular protest movement in 2007, which later made calls for separation, ICG said.
Many southerners complain northerners based in the capital Sanaa have discriminated against them and usurped their resources for decades. Most of Yemen's fast-declining oil reserves are in the south. The central government denied allegations of discrimination.
Southern Yemen has also been affected by al Qaeda-linked militants, who seized several towns in Abyan governorate in 2011, including the governorate capital Zinjibar.
Zinjibar was nearly destroyed in clashes between government forces and militants, and tens of thousands fled.
The militants carried out public summary executions, amputations and flogging during their rule, and the military used excessive force as it fought back, Amnesty International said.
When the situation in Abyan worsened, local tribes began to turn against the Islamists and joined government forces in an effort to push them back, ICG said.
Saleh held up the Islamists' sudden success as an example of what al Qaeda would do if Yemen slipped further into chaos. But opponents suspected he had given a signal to militants, with whom the government was in contact, to make their move because he felt it would strengthen his case with the West for political survival.
In May 2012, after Saleh had stepped down, the government launched a major U.S.-backed offensive and regained control of the towns in June 2012.
The Islamist militants include Ansar al-Shari'a (Partisans of Islamic Law) and al Qaeda in the Arabian Peninsula (AQAP).
AQAP was formed when the Saudi and Yemeni branches of al Qaeda merged in 2009. It is based in Yemen.
The United States has been using drones to strike the Islamist militants, but discontent at their use has been growing. Armed tribesmen have held protests, saying the strikes kill innocent civilians, and some say they are an infringement of sovereignty.
Mass protests began in early 2011 demanding the end of President Ali Abdullah Saleh’s 33-year rule and these, combined with growing violence by Islamist and tribal militants, meant the government lost control of chunks of the country for several months.
Tens of thousands of people were displaced in southern, central and northern areas. Public services in most of the country stopped, and the unrest created severe fuel shortages and dramatically pushed up the price of food.
The number of malnourished children under the age of five nearly doubled to 750,000 as a result of the political turmoil, the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said in February 2012.
The 2011 protests against Saleh paralysed the country. Some of his top aides, military commanders, cabinet ministers and diplomats defected to the protesters' side.
Houthis carved out their own domain in the north, and al Qaeda militants seized towns in the south.
Fighting involving government forces and rebels, Islamist militants and rival tribesmen affected several parts of the country, mainly the capital Sanaa and the southern and northern regions.
Tribesmen attacked and closed the main oil pipeline in the oil-producing Maarib province, near Sanaa, in 2011. They blockaded the area, costing the government millions of dollars a day in lost exports and sparking a severe fuel crisis, power outages and soaring prices.
After surviving an assassination attempt in June 2011, Saleh went to Saudi Arabia for medical treatment. Under a deal brokered by the Gulf Cooperation Council, he finally agreed in November to hand over power to his deputy, Vice President Abd-Rabbu Mansour Hadi, and a unity government was formed.
The deal brought some calm to Sanaa, but violence continued in other parts of the country, especially the governorates of Sa'ada and Hajjah in the north, and Abyan and Aden in the south.
In January 2012 parliament granted Saleh full immunity from prosecution, and a month later presidential elections were won by Hadi, the sole candidate.
The Yemen Times gives news in English, with detailed reports of clashes and sieges.
The BBC profile includes links to other media.
For the latest U.N. Office for the Coordination of Humanitarian Affairs reports, visit ReliefWeb.
The Carnegie Endowment for International Peace has published research on Yemen.
Human Rights Watch regularly monitors the situation in Yemen.
London-based think tank Chatham House also produces occasional briefing papers on Yemen.
The U.N. Children's Fund (UNICEF) tracks the plight of children in conflict-affected areas as well as the country as a whole.
The U.N. Refugee Agency (UNHCR) monitors refugees, and the Internal Displacement Monitoring Centre monitors those displaced by Yemen's internal conflicts.
The World Food Programme (WFP) has useful information about Yemen's food needs.