The three underlying causes were ethnic disintegration, economic volatility and declining empires. The question now is whether the 21st century is likely to be as bloody.
There is less economic volatility. Innovations such as inflation targeting have helped governments limit rises in consumer prices, and organisations such as the IMF and WTO have helped avert trade disputes. However, the Middle East has the capability to launch a new era of violence: it has economic volatility, imperial conflict and ethnic disintegration. Iraq is currently one of the hotbeds: its economic growth slumped in 2003, the year the US invaded, rose in 2004 and has more recently slowed. The ethnic conflict is more a clash within civilisations (Shia versus Sunni) than a clash between civilisations. The escalating civil war may spill over into neighbouring countries such as Iran. This nightmare scenario is already more likely than one of peace.
The next war of the world
Foreign Affairs, September/October 2006