Top 15 least peaceful nations:
1 Somalia  -  2 Iraq  -  3 Sudan   -  4 Afghanistan  -  5 DPR Korea  -  6 DR Congo 7 Russian Federation  -  8 Pakistan   -  9 Israel  -  10  Central African Republic 11 Libya  -  12 Nigeria  -  13 Chad  -  14 Zimbabwe  -  15 Colombia

Sub-Saharan Africa remains the region least at peace, containing 40% of the world's least peaceful countries

Threat of Terrorism Climbs: Despite the decade long War on Terror, the likelihood of terrorist attacks has increased in the past year in 29 countries.

Somalia displaces Iraq as world's least peaceful nation

Violence cost the global economy more than $8.12 trillion in 2010

Defining peace - Positive/Negative
The concept of peace is notoriously difficult to define. The simplest way of approaching it is in terms of harmony achieved by the absence of war or conflict. Applied to nations, this would suggest that those not involved in violent conflicts with neighbouring states or suffering internal wars would have achieved a state of peace.

This is what Johan Galtung1 defined as a "negative peace"- an absence of violence. The concept of negative peace is immediately intuitive and empirically measurable, and can be used as a starting point to elaborate its counterpart concept, "positive peace".

Having established what constitutes an absence of violence, is it possible to identify which structures and institutions create and maintain peace? The Global Peace Index (GPI) is a first step in this direction; a measurement of peace as the "absence of violence" that seeks to determine what cultural attributes and institutions are associated with states of peace.
               
About the Global Peace Index (GPI)
The GPI, produced by the Institute for Economics and Peace, is the world's leading measure of global peacefulness. It gauges ongoing domestic and international conflict, safety and security in society, and militarization in 153 countries by taking into account 23 separate indicators.
http://www.visionofhumanity.org/info-center/global-peace-index-2011/