The British did become an occupying force, but refused to give in to Shia demands for a major role installing instead a royal dynasty.
Between the creation of the modern Iraqi state in 1921 and the overthrow of the monarchy by the army officer Abd Al-Karim Qasim in 1958, there were 23 governments, four of them headed by Shia prime ministers.
Qasim became the first prime minister of the Republic of Iraq. He tried to satisfy the Shia, who comprised the majority of the Iraqi Communist party that Qasim sympathised with.
However, after Qasim had ordered the execution of several senior army officers, he was toppled in 1963 by his old companion Abd al-Salam Arif, who was an Arab Sunni. Arif was killed in a helicopter crash in 1966 and was succeeded by his brother Abd Al-Rahman Arif.
In 1968 Arif was in turn toppled by the Baathists, and Ahmad Hasan al-Bakr, an Arab Sunni, became the president of Iraq. In 1979 he was succeeded by his fellow citizen Saddam Hussein.
Commitment in question
The Shia failed to gain senior positions during the second half of the 20th century. Successive Iraqi governments accused the Shia of being loyal to neighbouring Iran, and doubted their commitment to Iraqi nationalism.
The major Shia revolt against what they described as an anti-Shia Iraqi Sunni government was in 1991. As the Iraqi army was retreating from Kuwait, they took tens of thousands of unarmed Iraqi soldiers by surprise.
The holy city of Karbala is a
centre for Ashura events
The whole of southern Iraq was in a state of revolt and the Iraqi republican guard, Iraq's most loyal and professional soldiers, had to intervene to quash the rebellion.
The Iraqi army was accused of using excessive force in their attempts to control the Shia uprising, which left a deep scar in the relations between Iraqi Shia and the government.
Thousands of Iraqi Shia fled the country and became fierce opponents of Saddam Hussein's rule.
The Shia opposition did not hide its desire to see the Sunni Saddam Hussein toppled, even at the hands of a foreign force.
Iraqi political analysts and intellectuals blamed the increasing hostility between Shia and the Iraqi government on Shia Iran.
When Saddam Hussein was removed by US-led forces on 9 April 2003 Iraqi Shia breathed a sigh of relief. Although Shia raised the slogan of "peaceful resistance" to the occupation, their militias have given a clear indication that they are keen to have the lion's share of power this time.
Iraq's history has been free from sectarian conflicts. Yet, after the occupation of Iraq there have been signs of growing sectarian tension and divisions.
In August 2003 the prominent Iranian backed Shia cleric Muhammad Baqir al-Hakim was assassinated in a massive car bomb attack in Najaf. A high-profile Arab Sunni cleric was assassinated in Baghdad last February.
Sunni mosques have been taken over by Shia in several Iraqi cities. Both Shia and Sunni mosques were attacked after the fall of Baghdad.
Many Iraqis insist there is no hatred between Sunni and Shia and blame foreign powers for trying to provoke a sectarian war.
The main tribes contain both Shia and Sunnis and intermarriage has been a marked feature of the country's history.
Muslim Sunni and Shia scholars in Iraq have been at pains to smooth over divisions between the two sects, like exchanging mosques during prayers and holding joint meetings.