When it comes to crossing international frontiers, there's one travel document that opens more doors than any other.

And it isn't a U.S. passport.

German citizens, it seems, have the potential for the greatest mobility in the travel world.

With a German passport, travelers can enter 177 out of 218 countries and territories without a visa, according to the 2016 Visa Restrictions Index.

 The list, compiled annually since 2006 by London-based consulting firm Henley and Partners and the International Air Transport Association, ranks nations by how freely their citizens, unencumbered by immigration red tape, can explore the planet.

This year, it shows that citizenship of a superpower doesn't carry the clout it once did.

The United States, which ranked first in 2014 and 2015, has now dropped to fourth place.

Immediately behind Germany, holding its position as runner-up for the second year running, is Sweden with visa-free access to 176 countries.

Finland, France, Italy, Spain, and the United Kingdom -- which had topped the list since 2013 -- are now tied for third place, making Northern and Western European citizens the most privileged in international travel.

Japan and South Korea were also among the group in the top three in 2014 and 2015, but have slid down to fifth and sixth place respectively this year.

Belgium, Denmark and Netherlands stand alongside the U.S. in fourth.

At the bottom of the list, labeled countries with the "worst passports," are Afghanistan, at 104, followed by Pakistan, Iraq, Somalia, and Syria.

Courtesy CNN