nuclear weapons

A U.N. treaty outlawing nuclear weapons went into effect on Friday, having been ratified by at least 50 countries. But the ban is largely symbolic: The U.S. and the world's other nuclear powers have not signed the treaty.

The two-minute warning that had held over the past two years has now shrunk to 100 seconds before midnight on the Doomsday Clock set by the Bulletin of the Atomic Scientists.

With the holiday just days away and no sign of a diplomatic breakthrough in sight, here are what experts say are the possibilities for North Korea's "Christmas gift."

Pyongyang did not elaborate on the statement, but in 2017, state media referred to North Korea's first test launch of an ICBM as part of a "package of gifts" for the U.S.

The nuclear arms race wastes resources that could instead improve people's lives and protect the environment, the pontiff said. His tour marks the first papal visit to Japan in nearly 40 years.

The Intermediate-Range Nuclear Forces Treaty was signed in 1987 by President Ronald Reagan and Soviet leader Mikhail Gorbachev. The U.S. has long accused Russia of refusing to comply with its terms.

President Trump greeted North Korean leader Kim Jong Un at the Demilitarized Zone that separates the two Koreas. He briefly stepped over into North Korea, a first for a sitting U.S. president.

Talks between President Trump and North Korean leader Kim Jong Un ended early Thursday. Trump cited continued sanctions against North Korea as a sticking point.

The U.S. and Russia seem increasingly interested in battlefield nuclear weapons. Arms control advocates fear a return to the darkest days of the Cold War.

The Rocky Flats National Wildlife Refuge sits on more than 5,000 acres of trees, wetlands and pristine rolling prairie about 16 miles northwest of Denver. It hosts 239 migratory and resident species, from falcons and elk to the threatened Preble's meadow jumping mouse. It also used to be the site of a federal nuclear weapons facility — and it's reopening to the public this weekend.