A World War is a war involving more than 2 continents, in which at least 20 major countries participate in an attack against a common enemy, and which has the attention of the average civilian, due to the significant loss of life. A lot of theorists claim that the terrorist attack on the World Trade centers and subsequent war with Iraq is the beginning of WWIII. Initially 40+ countries were a part of the coalition that invaded Iraq. As of August 2010, 4,733 Coalition (including US) soldiers had been killed in Iraq. The US deaths made up 4,415 of those deaths. Since the beginning of the U.S. reconstruction effort, 224 U.S. civilians have died in Iraq (2007 report.)
The Cuban Missile Crisis (in 1962) is generally thought to be the point at which the risk of World War III was closest. With the globalization of the marketplace and trade and the spread of nukes, it has become increasingly costly and suicidal to start WW3. So in theory, nations are, more than ever, unlikely to start wars, yet here we are on the brink of another war with Iran. Ever increasing oil prices, economic depression, North American union and the declaration of martial law within the US are all, supposedly, factors that will contribute to the next world war.