(Adds details on govt clan system)
Dec 5 (Reuters) - Somalia's new cabinet has run into trouble this week, as five ministers quit claiming their clans were under-represented.
Here are some facts about clans, the key to understanding Somalia's history, society and above all, politics:
WHY ARE CLANS IMPORTANT?
* The clans control districts and businesses and are the arbiters of most aspects of Somali life. Decisions are made collectively within the clans and their complex sub-divisions.
* An internationally recognised interim government formed in 2004 was created on a "4.5" clan structure, meaning major positions were split between the four main clans. The remaining 0.5 share was given to a grouping of smaller clans sometimes called the Fifth Clan.
* Some Somali nationalists argue that the 4.5 system has had the effect of fracturing Somalia on clan lines by imposing a federal system. They say that system -- historically a solution for uniting ethnically diverse countries like Ethiopia -- is totally unsuited for Somali, one of the most ethnically unified countries in sub-Saharan Africa.
MAIN CLANS AND THEIR PLAYERS
1. HAWIYE CLAN:
* New Prime Minister NUR HASSAN HUSSEIN hails from the ABGAL sub-clan, same as his predecessor ALI MOHAMED GEDI -- who resigned under pressure.
* SHEIKH HASSAN DAHIR AWEYS, now exiled in Eritrea after the government and Ethiopian troops defeated his militant Islamist movement in January, is from the AYR wing of the HABR GEDIR sub-clan. Aweys' Afghanistan-trained protege ADEN HASHI AYRO, said to be leading the Mogadishu insurgency, is also an AYR.
2. DAROD CLAN:
* Ex-dictator MOHAMED SIAD BARRE, ousted in 1991, came from the MAREHAN sub-clan.
* President ABDULLAHI YUSUF is from the MAJERTEEN wing of the clan. Since he is a Darod, the prime minister must be Hawiye.
3. DIR CLAN
* The education minister ISMAIL HURRE BUUBA is from the Dir sub-clan of IDAGALE.
4. DIGIL AND MIRIFLE CLAN
* This clan also known sometimes as RAHANWEIN. Four of the resigning ministers came from this clan. Parliamentary speaker SHEIKH ADAN MADOBE comes from this line via the HADAMO sub-clan.
5. FIFTH CLAN
* Prof. MOHAMED OMAR DALHA, the deputy parliament speaker, is a member of this clan via the JARERERWEYNE sub-clan. The fifth resigning minister also comes from this group. That sub-clan is made up of Somalis from the ethnic Bantu minority originally brought to Somalia by slave traders, from what is now Mozambique, Tanzania and Malawi.
CLAN ROLES IN RECENT HISTORY
* Hawiye dissatisfaction has played a major role in the travails of the interim government since its inception in late 2004. Many Hawiye felt that Gedi was imposed on them as prime minister by Ethiopian pressure, hence cheating them of real influence in the clan's top government position. That dissatisfaction manifested itself in an Islamist movement that controlled Mogadishu for the latter half of 2006, until its defeat by Ethiopia and Somalia over the New Year. Some Hawiye are still involved in the current insurgency. It remains to be seen what welcome the clan will give the new prime minister.
* Somalia's last national president, dictator Siad Barre, was blamed by many Somalis for favouring members of his Marehan sub-clan and discriminating against others, often brutally. That spurred Darods in northeastern Somalia who felt marginalised to rise up against his government, followed by Dir from what is now self-declared Somaliland. Barre's actions are said by Somalis to underpin much of the current Darod-Hawiye mistrust.
Sources: Reuters, Somali experts. (Writing by Andrew Cawthorne, Bryson Hull and Guled Mohamed, editing by Mary Gabriel)