The Scandinavian countries among the most peaceful countries in the world. According to the published ranking of the Global Peace Index 2013 Denmark was ranked in second place out of 162 countries (just behind Iceland), Finland 7th, Sweden took the 9th place, Norway 11th.
Poland is at the 25 position.
The report takes into account, inter alia, the political stability of the country, the perception of criminogenic phenomena, terrorism, access to weapons, violent demonstrations, violent crime, defense expenditure, the number of people serving in the army, the state's defense, nuclear weapons, and others.

The entire report with a detailed description:

Global Peace Index
The world’s leading measure of national peacefulness,
the GPI measures peace according to 22 qualitative and quantitative indicators.

Source, photo: visionofhumanity.org/#/page/indexes/global-peace-index