The devastating war escalated in 2015 when a Saudi-led military coalition intervened on the side of the government.
PIC: A Yemeni man walks by burning tyres as protesters demonstrate against inflation and the rise of living costs in Aden on Saturday. (AFP)
Impoverished Yemen has been mired in deadly conflict between Shiite Huthi rebels and troops loyal to President Abedrabbo Mansour Hadi since 2014.
The devastating war escalated in 2015 when a Saudi-led military coalition intervened on the side of the government after the rebels seized the capital and several provinces.
UN-sponsored peace talks between the two sides in Geneva failed to materialise last week, as a defiant call for "resistance" by the top Huthi leader on Saturday sparked fears of an escalation.
Here is an overview:
Rebellion in Sanaa
In July 2014, Huthi fighters, who have opposed the central government for a decade, launch an offensive from their northern stronghold of Saada.
In September, they enter the capital Sanaa, seizing the government's headquarters and state radio after days of fighting.
The rebels ally themselves with military units loyal to ex-president Ali Abdullah Saleh, who was forced to quit after a 2011 uprising.
In October, they capture the vital Red Sea port of Hodeida.
In January 2015, after fierce battles in Sanaa, the Huthis seize the presidential palace and surround the residence of the new president, Hadi, who flees south to the city of Aden.
Saudi air strikes
A Saudi-led coalition enters the conflict in March 2015 with air strikes on rebels.
The Huthis are aligned with Iran, a bitter rival of Sunni power Saudi Arabia.
As the rebels advance on Aden, Hadi quits the city amid intense fighting and takes refuge in the Saudi capital, Riyadh.
In July, his embattled administration announces its forces have retaken the entire province of Aden, their first success since the coalition intervened.
The city of Aden becomes the country's de facto capital, with Sanaa still under rebel control.
By mid-August, pro-government forces have retaken five southern provinces, but face new threats with the growing presence of Al-Qaeda's Yemen branch and the emergence of the Islamic State group.
In October, government forces reclaim control of the Bab al-Mandab Strait, an internationally vital Red Sea shipping route off Yemen's coast.
Rebels kill ex-president
In August 2016, lengthy UN-brokered negotiations in Kuwait between the government and rebels collapse after failing to broker a power-sharing deal.
Splits emerge in the rebel camp in 2017 after Saleh makes overtures to the Saudi-led coalition. Armed clashes rock Sanaa and in December the former president is assassinated by his former Huthi allies.
Divisions also emerge among pro-government forces, with fighting in Aden in January 2018 between southern Yemen separatists and other factions loyal to the president.
Advance on vital port
In June 2018, government fighters, backed by Saudi and Emirati forces, launch an offensive to retake the rebel-held port of Hodeida, a vital entry point for food imports and international aid.
Within days they say they have taken control of the city's airport, but they pause their advance to allow negotiations.
The war has killed nearly 10,000 people, with a particularly heavy toll on civilians caught up in air strikes often blamed on the coalition.
In one of the most severe incidents, a strike on a wedding hall in the Red Sea town of Mokha in September 2015 killed around 131 people. The coalition denied responsibility.
In October 2016, a coalition air strike killed 140 people at a funeral in Sanaa.
This August, 51 people including 40 children were killed in a coalition air strike on a bus in a crowded market in the rebel-held north.
The coalition admitted afterwards "mistakes" were made.
On August 23, a further 26 children were killed by coalition air strikes near Hodeida.
The coalition admitted later there may have been "collateral damage".
Peace talks falter
Long awaited UN-sponsored talks between the Saudi-backed government and the rebels were expected to begin in Geneva on September 6.
But the Huthi delegation refused to leave Sanaa, saying the UN had failed to guarantee its safe return and to secure the evacuation of wounded rebels to Oman.
On September 8, the government delegation left Geneva, as talks faltered before they could begin and renewed fighting broke out around Hodeida.
Rebel leader Abdulmalik al-Huthi defended his decision not to send a delegation to Geneva, calling for "steadfastness and resistance to aggression on all fronts".