War should be understood as an actual, intentional and widespread armed conflict between political communities, and therefore is defined as a form of political violence or intervention.
The set of techniques used by a group to carry out war is known as warfare. An absence of war is usually called peace.
The deadliest war in history, in terms of the cumulative number of deaths since it's start, is the Second World War, with 60–85 million deaths.
Some of the biggest wars have been fought because of religious reasons, however, out of 1763 recorded wars, only 1223 (7%) of them had a religious cause!
Apparently most people seek other things than trying to prove a point of view.
