When social and political processes break down, marauding gangs prey on local populations. Strong and charismatic leaders may pull together such groups. The most successful then can effectively be described as warlords who are a rule unto themselves. They function as chieftains protecting their own territory and endeavouring to extend their territory at the cost of others.
Recent examples are Lebanon, where at least 12 separate private armies were fighting each other in the south in the 1980s; Somalia, which gave rise to the UN intervention in 1992; Afghanistan, where mojahedin faction chiefs command bands of the holy warriors in the jihad that began in 1992. Warlords were also a feature of the Liberian civil war in 1996.
Aggravated by 
(D) Detailed problems