LONDON With Muammar Gaddafi effectively forced from power, Libya's complex tribal and cultural divisions could hinder attempts by the Benghazi-based rebel leadership to impose its rule on the country.
At worst, some analysts said the country could face a bout of ethnic infighting that residual Gaddafi loyalists may exploit, complicating attempts to rebuild the country, resume oil exports and return to relative peace.
Libya has long been divided between various ethnicities and groups including North Africa's indigenous Berber inhabitants, Arabs who arrived later and ethnic African tribal groups from further south. Cultural divisions between its two major cities of Tripoli and Benghazi can be traced to before the Romans.
"The prospect of increased friction or violent conflict between the country's tribes, clans and ethnic groups -- specifically between the Arabs and Berbers -- remains a serious source of concern," said Anthony Skinner, Middle East analyst at political risk consultancy Maplecroft.
"The general absence of formal structures through which to govern poses another challenge."
With some reports of reprisal attacks against individuals and groups accused of backing Gaddafi, analysts said divisions could worsen if law and order are not restored in the coming weeks.
Below is a summary of some of the main tribal and regional divisions within Libya.
Coastal Libya has been divided into two distinct provinces since before the time of the Romans -- Tripolitania in the west around Tripoli and Cyrenaica around Benghazi.
In its early stages, the conflict divided Libya once again along those lines, with the area around Benghazi under opposition control and the rebels taking the flag of the former Cyrenaican monarchy ousted by Gaddafi.
Benghazi-based rebel forces struggled to push Gaddafi loyalists back beyond the traditional provincial tribal boundary near the oil port of Brega, leaving it to western Libyan rebels -- many ethnic Berbers -- to take the capital Tripoli.
Experts say opposition to Gaddafi was always higher in eastern areas although several western tribes repeatedly rebelled against him. Gaddafi's support was strongest in his own tribe as well as southern, often African tribes from Libya's old desert province of Fazzan.
ETHNIC, TRIBAL DIVISIONS
Political risk consultancy Stratfor estimates that Libya has up to 140 tribes, but only 30 have any particular significance.
Some Libyans, mostly in the rebel movement, say such traditional structures are not very important in urban areas, but others say that they may prove vital in the absence of traditional government structures.
Tribes, subtribes and other groups have a variety of leadership structures, and rarely simply function as monolithic blocks, analysts say.
Below are some of the main tribes and other ethnic groups with details provided by analysts and Reuters reporters around the region.
Gaddafi's tribe is one of Libya's smaller groups and not particularly powerful historically. With its territory running from the port of Sirte midway between Tripoli and Benghazi down into the Sahara, he used it to help cement his power.
Analysts say the tribe became wealthy under his rule, is sometimes accused of having a stranglehold on power and makes up the core elements of some of the "regime protection units." But some members -- perhaps part of assorted subtribes that benefited less from his rule -- may have abandoned him early in the uprising.
The rebels' National Transitional Council (NTC) has made contact with some members of the group, but analysts say that reprisals or attacks against those believed to have been loyal to Gaddafi could cause problems.
Usually estimated to be Libya's largest tribe with up to one million of the total roughly 6 million population, tribal elders announced early on that they were turning against Gaddafi.
The tribe is based primarily to the east of Tripoli with its origins in Misrata, initially besieged by Gaddafi's forces and home to some of the rebels who took Tripoli. Some of their territory reaches toward Sirte. The tribe launched a coup against Gaddafi in 1993 with the support of the Magarha tribe demanding greater representation in government.
Although the coup failed and a number of leaders were killed, imprisoned and driven into exile, the tribe maintained sizeable numbers within the military. The tribe includes six subtribes and has sometimes suffered from internal divisions.
Analysts say this tribe is the second largest and it has had mixed relations with Gaddafi's government. Originally from the interior, many members have moved to the coast as the tribe has played an increasingly central role in politics. Leader Abdessalam Jalloud was once seen as the second most important man in the country, but he fell out with Gaddafi in the 1990s and the tribe joined the 1993 uprising.
After the coup failed, the tribe was able to maintain closer relations with Gaddafi following closed-door negotiations.
The traditionally nomadic Tuareg is divided between a number of states in the Sahara whose borders they do not recognize. Analysts estimate just over 560,000 live within Libya.
Tuareg rebels have attacked other Saharan governments and oil installations in pursuit of independence but have traditionally not clashed with the Libyan government, leading to some to suspect that Gaddafi armed them.
Libyan officials have offered asylum to non-Libyan Tuareg. They were believed to be broadly loyal to Gaddafi in the conflict, although again details are sparse. Some suspect Gaddafi may try to hide among them in Libya's desert south or use his contacts with them to sneak across the Southern border out of the country.
Estimated to make up to 50 percent of the population of the western mountains, the Berbers were seen as largely marginalized under Gaddafi's rule in favor of the majority Arabs. Many of them helped take Tripoli.
The NTC specifically targeted this group -- which was key to their victory -- and their draft constitution makes it clear they will be viewed as equal to their Arab counterparts.
For now, there seems to have been little in the way of tension between Berber and Arab rebels, but some say it might emerge in due course.
Gaddafi's second wife came from this eastern tribe and many of his children are believed to support it, with some members being appointed to mid-level bureaucratic posts. While many members quickly went over to the opposition, the tribal leaders appeared reluctant to make overt statements as to their loyalty during the uprising.
Largely rural and living in oil-producing regions of the east and interior, the tribe is relatively small but might demand greater say in the use of oil revenues. They are reported to have been among the most vocal opponents of Gaddafi during the uprising, and are said to be relatively well armed. Ultimately, their main interest is seen to be ensuring they continue to benefit from Libya's oil.
OTHER EASTERN TRIBES
The Misrata are said to be the largest tribe in eastern Libya, based around the eastern town of the same name (not to be confused with the identically named western town besieged by Gaddafi earlier in the war) and the cities of Benghazi and Darnah.
The al-Awaqir is most prevalent in the city of Al Bayda, home of NTC Chairman Mustafa Abdel Jalil, and has long been at the center of opposition to Italian and Ottoman colonialism.
The Obeidat are clustered around the northeastern garrison town of Tobruk. Several senior officials from this group publicly defected at the beginning of the uprising.
Rebel military leader Abdel Fattah Younes -- killed in an attack by other rebels -- was a member of this group, but Jalil was keen to appear alongside tribal leaders immediately afterwards and serious divisions looked to have been avoided.
OTHER WESTERN TRIBES
The Bani Walid overlap geographically with the Warfalla, and was reported to have defected from military units early in the uprising.
The Tarhuna make up roughly a third of the population of the capital Tripoli, while the Zentan are located between Tripoli and the Tunisian border. Both tribes are said to be heavily represented in the military but members were also reported to have joined early protests. Sources: risk consultancies Stratfor, AKE, Maplecroft, Control Risks, Reuters
(Reporting By Peter Apps; editing by Elizabeth Piper)