Yemeni fighters loyal to the country's president Abedrabbo Mansour Hadi pose for a picture with weapons in the Dabab district in Taez province, southern Yemen on December 13, 2015
Sanaa (AFP) - Armed groups have led the slide into chaos in Yemen, where a truce between Arab-backed loyalist forces and Iran-backed Shiite rebels is expected to enter into force at midnight Monday.
Shiite militiamen and Sunni extremists have sought to exploit a power vacuum since 2011 nationwide protests forced veteran president Ali Abdullah Saleh to step down.
The Shiite Huthi militiamen, also known as Ansarullah (Supporters of God), have long complained of marginalisation by authorities in Sanaa.
They hail from the Zaidi sect, an offshoot of Shiite Islam that comprises approximately one-third of Yemen's Sunni-majority population.
Their strongholds lie in northern provinces bordering Sunni powerhouse Saudi Arabia, which is leading the Arab coalition against them.
North Yemen was a Zaidi imamate until a 1962 coup turned the country into a republic.
Badreddin al-Huthi, who formed the "Faithful Youth" political movement in 1992 to fight discrimination, is regarded as the spiritual leader of the Huthis who have taken his name.
His son Hussein led a nearly three-month uprising in Saada province before the army killed him in 2004.
Hussein's brother Abdulmalik now leads Ansarullah.
Six wars fought with the central government between 2004 and 2010 killed thousands of people before a truce was agreed.
The Huthis seized control of Sanaa on September 21, 2014 after months of clashes with the Sunni Islamist party Al-Islah.
They are accused of receiving support from Shiite Iran and backing from Saleh loyalists.
In March, they advanced on second city Aden, where UN-backed President Abedrabbo Mansour Hadi took refuge after escaping house arrest in Sanaa.
But the Saudi-led coalition helped pro-Hadi forces push the rebels out of Aden in July, as well as four other provinces.
Loyalists and allies
Yemen's armed forces have been severely weakened due to mass defections by troops that remained loyal to Saleh.
But Hadi loyalists have been boosted by the Popular Resistance forces -- an alliance of southern separatists and local tribesmen.
Southern separatists have long called for the secession of the formerly independent South Yemen. But they have taken up arms alongside Hadi's loyalists after the rebels advanced on their regions.
Pro-government forces have gained the upper hand in the south and Marib, east of Sanaa, thanks to strong support by the Saudi-led coalition.
The United Arab Emirates plays a key role in the coalition, which also comprises Bahrain, Egypt, Morocco, Qatar and Sudan.
Al-Qaeda in the Arabian Peninsula (AQAP) is regarded by the United States as the extremist network's deadliest branch.
It was formed in 2009 when Al-Qaeda in Yemen -- behind the 2000 bombing of the USS Cole in Aden harbour that killed 17 American sailors -- merged with its Saudi counterpart.
AQAP has strongholds in south and southeast Yemen and has repeatedly attacked Yemeni security forces and been targeted by scores of US drone strikes.
The group also abducts foreigners, including US journalist Luke Somers and South African teacher Pierre Korkie, killed by their captors when US commandos stormed an AQAP hideout last year.
AQAP also claimed responsibility for the deadly January 7 attack in Paris on French satirical magazine Charlie Hebdo, targeted for its cartoons of the Prophet Mohammed.
With state institutions weakened, AQAP has become the only force capable of resisting the advance of Ansarullah.
Sunni tribes, hostile to a Huthi advance into their provinces, have teamed up with Al-Qaeda against the militia, with the government mostly standing by.
Since September last year, AQAP has claimed several attacks on the Huthis, including the killing of 49 people in the central province of Ibb in December and another in October that left 47 dead in Sanaa.
Islamic State group
An emerging force in Yemen after claiming several deadly bombings against Huthis and government officials, including the killing of Aden's newly appointed governor Jaafar Saad in early December.
The group claimed multiple suicide bombings in March that targeted two mosques in Sanaa attended by Huthis, killing 142 people and wounding more than 350.
The claim by IS represents a strong show of force for the jihadist group as Yemen has been always considered the playground of its rival Al-Qaeda.