The most common cause of war is poor leadership. All it takes is for the king/president/tyrant to make a few mistakes, and there you have a war. The damn things are easy to start, but so hard to stop. So it should come as no surprise that nations that are poorly run, are the most prone to being embroiled in wars or other internal violence. A recent NGO survey of "Failed States" came up with a lest led by Sudan, Congo, Ivory Coast, Iraq, Zimbabwe, Chad, Somalia, Haiti, Pakistan and Afghanistan. All are currently undergoing wars or serious internal disorder. This should come as no surprise, as the ranking for the "failed states" concentrated the ability of the government to maintain order, and sustain economic activity and growth. That means rule of law, and efficient government services.
Doing these rankings is regular favorite with political science groups. It's an easy target, because there is such a clear and direct link between effective national leadership, and peace and prosperity. Despite that, why do so many dysfunctional countries continue to exist? Partly it's because many parts of the world are still making the transition from tribal or monarchy cultures, to what we call the "nation state". The older tribal and monarchy (feudal) forms rely on family ties, not democracy, for selecting leaders. This does not work well in the long run, and is prone to frequent civil wars. The tribal cultures also tend to have a lot of factionalism, and often well armed and aggressive factions as well.
Adding to the confusion is that nearly everyone says they have a functioning nation state, even when they don't. So many countries put a lot of effort into pretending they are a functioning nation state. Many of the nations who earn the "failed state" category provide a strange experience for visitors. Government officials pretend they know what they are doing, when they do anything at all. But it's all old school, where the rules are made up as you go along and it's every clique for itself.
"Law and Order" means that disputes are settled via courts, not the extended use of guns. A failed state has no functioning legal system. It usually has what looks like a legal system, but it's just for show, and outcomes are bought, or otherwise arranged via knowing the right people.
The lack of law and order and a legal system makes it impossible for the economy to thrive, thus there is a lot of poverty. That provides an ample supply of young gunslingers. So all those wars in failed states should come as no surprise. The corruption in failed states is often of epic proportions. For example, even though the Iraqi government estimates that $4.2 billion of oil revenue (about 20 percent of the total) was stolen last year, more was spent on infrastructure and government services last year than in any year during the last two decades of Saddam's rule. Saddam was a master thief, and corrupt to the core.
Turning a failed state into a functioning one is a combination of leadership and mass acceptance of personal responsibility for making a nation state work. Many people in failed states know this, but making it happen has proved difficult. Greed and fear of change keep the old, bad, ways in play.