The Global Peace Index, created by the Economist Intelligence Unit, is based on 24 indicators measuring peace inside and outside of a country. They include the number of wars a country was involved in the past five years, how many soldiers were killed overseas and how much money was made in arms sales. Domestic indicators include the level of violent crimes, relations with neighboring countries and level of distrust in other citizens.
This are the maps for 2009 and 2010:
Here’s another version: