Albania has traditionally been divided into two tribal groups: the Ghegs who live in the north and spread into Kosovo and western Macedonia, and the Tosqs from the south. Their differences are primarily linguistic; the Ghegs speaking a rougher, less sophisticated variety of Albanian, but they are noticeable also in levels of education, living habits and religious practice.
The differences have seethed beneath the surface of Albanian politics since the country won independence from the Ottoman empire in 1912. They go a long way to explain why Enver Hoxha, the country's post-war Stalinist dictator, became so paranoid about Albania's sovereignty and the risk of subversion from abroad. Now they weigh heavily on President Sali Berisha, a typical Gheg born in a northern village, as he struggles to assert his authority on the half of the country with which he has little cultural connection.
The north-south dividing line is generally considered to be the river Shkumbin, which springs from Lake Ohrid on the border with southern Macedonia and flows in a straight line across the country before draining into the Adriatic half way between the country's two main ports, Durres to the north and Vlora to the south. This is also the frontline of the present conflict.
Tirana, the Albanian capital, belongs geographically in the north but by temperament is very much a part of the south - highly cultured, open to the outside world and suspicious of the secretive, essentially mafi- oso world of extended families and blood feuds that still operates in the north.
One of the reasons Mr Berisha was successful in portraying himself as a staunch anti-Communist is because he came from the opposite end of the country from Hoxha, who was born in Gjirokaster on the Greek border. Once installed as president in 1992, Mr Berisha brought thousands of villagers down from the north to take up jobs in ministries and in the security forces, especially the police and the Shik secret police.
Opposition parties, particularly the Socialists, have retained their heartland in the south - for cultural as well as political reasons - and strongly resent the influx of "northern savages" into the country's power structure. Whenever demonstrations have been violently broken up by police the anonymous assailants are invariably described as talking with thick northern accents.
Organised crime in Albania is also divided on tribal lines. Intelligence experts believe the Ghegs are involved in trafficking drugs and contraband cigarettes, using their secret networks - relying at least in part on Gheg state officials - to bring merchandise across the mountains from Kosovo and out through ports towards Italy.
The Gheg world operates, like Cosa Nostra in Sicily in its heyday, under a strict shroud of silence called Bessa and has its own code of classically mafioso behaviour called the Canun of Lek Dukagjeni, based on family honour and legitimate revenge through bloodshed. One of the reasons international crime fighters have found it hard to crack the Ghegs' activities is because nothing ever leaks out.
The Tosqs' main criminal activities, meanwhile, are based in Vlora and involve the highly lucrative smuggling of arms and illegal immigrants across the Adriatic to Italy. The fact that the present rebellion began in Vlora is no coincidence: the townspeople have the weapons behind them, as well as a mafia power structure virulently opposed to Mr Berisha's Gheg-dominated governing order.
The Gheg-Tosq rivalry is far more than an academic exercise in cultural differences; it has at different times threatened Albania's very existence. During the Second World War, the Greek army occupied most of Tosq Albania, and have at various stages had ambitions to annex it. In 1946, the US Congress made a notorious proposal, never followed through, to partition the country between Greece and Yugoslavia - again along the old fault line.
One reason Hoxha banned religion in 1967 was because of fears the Roman Catholic-influenced north could split from the mainly Muslim south. Religion has been drummed out of Albanians, but the cultural gulf has been widening ever since Communism was overthrown in 1990-91.