The index, now in its second year, ranks 140 countries according to their relative states of peace, based on factors such as military expenditure, respect for human rights and number of homicides per 100,000 people.

The latter statistic helps pull down the United States, which ranked 97th in the latest index, one place lower than last year.

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

"The U.S. does so badly because it has the highest proportion of jailed people in the world. And it has high levels of homicide and high potential for terrorist attacks," said Killelea, who added that "the index is not making any moral statements by the ranking."

More information on the report and the full index can be found on the website visionofhumanity.org.