Yemen's Shiite Huthi rebels, who signed a UN-brokered peace deal Sunday after seizing key institutions, only recently began extending their influence beyond their northern highland stronghold.
The rebels belong to the Zaidi sect, an offshoot of Shiite Islam which makes up approximately a third of the Sunni-majority country's population.
Zaidis are the majority in the northern provinces bordering Sunni powerhouse Saudi Arabia, and the Huthis are widely accused of receiving support from Shiite-dominated Iran.
The north was a Zaidi imamate until a 1962 coup turned Yemen into a republic ruled by a government long considered illegitimate by the rebels.
Badreddin al-Huthi, who formed the "Faithful Youth" movement in 1992 as a political group to fight discrimination, is considered the spiritual leader of the Huthi movement, which is named after him.
His son Hussein led a nearly three-month uprising in the northwestern province of Saada that left 400 people dead before the army killed him in September 2004.
The rebels are now led by Hussein's brother, Abdulmalik al-Huthi.
They fought six wars with the central government between 2004 and February 2010, when they signed a truce.
Thousands of people were killed in the rebellion.
- Role in 2011 uprising -
As an Arab Spring-inspired uprising against then president Ali Abdullah Saleh swept through Yemen in 2011, the Huthis reached out to the opposition in Sanaa and joined protest camps there.
It was their first major show of influence outside their strongholds in Saada and Amran provinces.
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However, the rebels rejected a Gulf deal brokered by Saudi Arabia, which fought them between 2009 and 2010 after a border incursion.
Under the deal, Saleh, himself a Zaidi who ruled Yemen since 1978, was replaced as president by Abdrabuh Mansur Hadi in 2012 and a consensus government was formed.
The rebels rejected the new government and repeatedly accused it of corruption. They chose a fuel price rise in late July as an opportunity to revolt.
The rebels had already been advancing out of the mountains and closer to Sanaa, widening their zone of control in a bid to win a bigger share of a future federal government.
Earlier this year, the rebels drove the influential Al-Ahmar tribe out of its bastions in Amran.
The federation was agreed following difficult national talks that ended in February. Despite taking part in the dialogue, the Huthis rejected plans for a six-region federation.
On August 18, they established camps inside Sanaa and on Sunday swooped on key institutions, including the government headquarters and military sites, after an apparent surrender by security forces.
- Iran's influence -
Yemeni authorities have repeatedly accused Tehran of backing the Huthi rebellion, and during protests the rebels chant Iran's famous Islamic revolutionary slogan "Death to America! Death to Israel!"
Their public discourse also appears heavily influenced by Hezbollah, Lebanon's powerful Shiite militia that is backed by Tehran.
At protest camps, they have displayed pictures of Hezbollah chief Hassan Nasrallah alongside others of Syria's embattled Tehran-backed president, Bashar al-Assad.
"For years, the Huthis have moved closer to Iran in terms of organisation, ideology, politics and media," said Samy Dorlian, a Yemen specialist at the Institut d'Etudes Politiques at Aix-en-Provence in France.
The Huthi rebels, who last year rebranded themselves as Ansarullah (Supporters of God), claim direct descent from the family of the Prophet Mohammed.