In 2011, world peace improved for the first time in three years. Incidents of terrorism fell and the global economic downturn decreased violence by reducing the amount countries spent on military budgets. However, while many parts of the world improved, others got worse as the result of rising commodity costs, increased protests and internal conflicts.

Read: The World’s Most Peaceful Countries
Read: The World’s Least Peaceful Countries 

Recently, The Institute for Economics and Peace released the sixth edition of their annual Global Peace Index. The report examines 158 third-world, developing and developed nations around the world based on 23 separate indicators that, combined, measure the relative level of internal and external conflict in a country.

According to the report, “peace is notoriously difficult to define,” but in its most basic form it is “harmony achieved by the absence of war or conflict.” According to the IEP, those countries that can avoid military or diplomatic conflict with other nations and maintain stability and safety within their own borders are peaceful.

The 23 components that comprise the Global Peace Index, or GPI, are broken into two categories. Internal conflicts, which accounted for 60% of the total score, included measures of criminality, violent demonstrations and terrorism in each country, as well as the presence of violent internal political conflicts. According chairman and founder of the IEP, Steve Killelae, “Internal indicators measure the internal peace of a nation. So to describe a perfect nation, there would be no crime, no one in jail, and no need for police. The most peaceful nation would have the least of all three.” The other category, external peace, included military capability, the importing and exporting of weapons, and diplomatic relations with bordering nations.

According to the report, the most peaceful nations in the world are primarily in Europe, including several Scandinavian countries. New Zealand, Japan and Canada are also among the most peaceful. The countries with the greatest levels of external and internal violence are primarily in Africa, Eastern Europe and the tumultuous Middle East.

Of the components that make up the index, some were much more likely to correspond with high levels of peace or the lack of peace than others. Countries with easy access to small arms were much more likely to be violent. The most violent countries in the world, including Iraq, Somalia and Afghanistan, are all rated by the Economist Intelligence Unit as having the greatest access to small arms.

The level of political terror in a country is also a major indicator for overall violence there, according to the report. Of the countries with the highest GPI score, all have among the highest levels of politically sponsored oppression, which comes in the form of imprisoning and murdering dissidents. The worst in this category include countries like the Sudan, the Democratic Republic of Congo and North Korea, all of which are scored as the least peaceful in the world. The countries with the highest peace ratings, including New Zealand and Canada, all have the lowest possible levels of political terrorism.

The IEP also considers several socioeconomic factors that are not themselves part of the rank, but that they measured as possible drivers of violence and peace. The data suggests that while a country’s GDP, adult literacy and unemployment do not appear to have a strong impact on peace, others appear to be directly related. The presence of civil liberties and freedom of the press have much closer relationships to peace, according to the report.

The clearest among these are political factors such as corruption. According Killelae, the relationship between corruption and the lack of peace is profound: Slight increases in corruption do not appear to affect slight increases in peace, but he says that once a tipping point is reached peace “just disappears.” While the IEP is not exactly sure why corruption is such a powerful indicator, Killelae suggests that it is near perfect measure of “just how well functioning the level of government is.”

Also Read: The 10 Best Countries for Entrepreneurs

According Transparency International’s measure, which IEP also considered, all but one of the most peaceful countries in the report has very low levels of corruption. Most of the least peaceful countries, including Somalia, Sudan and North Korea, have among the highest levels of corruption.

The Institute for Economics and Peace compiled more than 50 separate sets of data from a variety of sources, including the Economist Intelligence Unit, the World Bank, UNESCO, the World Economic Forum and Transparency International to measure aspects of peace. Using IEP’s original sources, 24/7 Wall St. reproduced data for the factors the report determined to have the strongest correlations nationally to the 23 measures of peace. Most of the measures, including the political terror scale, access to small arms, relations with neighboring countries, and likelihood of violent demonstrations, are on a scale of 1 to 5, with 5 representing the least peaceful and 1 the most peaceful.

These are the most- and least-peaceful countries in the world.