The US dropped 11 places to the 114th most-peaceful country out of 163 in this year's Global Peace Index published by the Sydney-based Institute of Economics and Peace, which also has offices in New York, The Hague and Mexico City.
And while terrorism levels jumped in Europe, it remained the most peaceful region on the planet.
Levels of peace around the world have improved slightly for the first time since the Syrian war began, but harmony has decreased in the U.S. and terrorism records have increased, a Sydney-based think-tank has found.
It said deaths from terrorism in countries that are in the Organisation for Economic Co-operation and Development (OECD) rose by more than 900% between 2007 and 2016.
Despite the declining United States score, terror attacks in Europe and conflicts in the Middle East, the world is actually becoming more peaceful, according to the study, with 93 countries listed as improving in this year's study, while 68 deteriorated. Among those were Denmark, Sweden, France and Turkey.
The most notable increases in the impact have been seen in highly economically developed countries, the latest edition of the Global Peace Index found. Researchers found that 60% of countries now have a higher rate of terrorism than they did 10 years ago.
It does not include the Manchester bombing last week, in which 22 people were killed in the worst terrorist atrocity in Britain since the July 7 attacks in London in 2005.
"Increasing inequality, rising perceptions of corruption, and falling press freedoms have all contributed to this substantial deterioration in the USA and an overall decline in peace in the North America region", he added.
The largest regional deteriorations in the score occurred in North America, followed by sub-Saharan Africa and the Middle East and North Africa (MENA). Before the outbreak of civil war there, it was the 65th least peaceful.
China, ranked 116th globally, Thailand (120th), the Philippines (138th) and North Korea (155th) were listed among the least peaceful in the world. Its fall has been the starkest of the past decade. Iceland, New Zealand and Portugal occupy the top three spots in 2017.