The index, now in its second year, ranks 140 countries according to their relative states of peace, based on factors such as military expenditure and respect for human rights.

The latest index released Tuesday ranked the United States at 97th, one place lower than last year and way below countries such as Costa Rica, Madagascar and Chile.

This year, Iceland is voted the most peaceful place, beating last year’s winner Norway. The United Kingdom is at 49, just below Panama. Unsurprisingly, Sudan, Somalia and Iraq are at the bottom of the list.

The idea for the index came from Steve Killelea, an Australian businessman and philanthropist who wanted to identify just what creates a peaceful country.

He asked the Economist Intelligence Unit to look at a range of variables, from levels of homicides per 100,000 people - which drags down America and boosts Denmark - to corruption and access to primary education.

“The U.S. does so badly because has the highest proportion of jailed people in the world. And it has high levels of homicide and high potential for terrorist attacks,” Killelea told The Associated Press. “Its overall score is a reflection of that. The index is not making any moral statements by the ranking.” Gavin Hayman, director of campaigns for Global Witness, a non-governmental organization that lobbies against corruption and human rights abuse, said the results were slightly skewed.

“The people who did this study only look at peace and the absence of war, and this approach may throw up some perverse readings,” he said.

“The U.S. has done some nasty things geopolitically, and it ranks poorly because of its high military spending, but that’s a little unfair as they are the ones that keep the world’s waterways free, and play a role in protecting global assets.”

Andrew Williamson, global director of client research at the Economist Intelligence Unit, said he hoped the index would be used by other researchers to look into why some countries stay more peaceful than others.

“The index is trying to measure the absence of peace. We are not looking at explanatory factors why some countries are more peaceful than others. We are inviting others to do this analysis themselves,” Williamson said.