Tensions between the United States and North Korea grew increasingly ominous last summer, when President Donald Trump warned of "fire and fury" directed toward the regime of Kim Jong Un.

Trump's bravado came hours after reports that North Korea had developed a nuclear weapon small enough to fit on a missile. In the days that followed, the escalating crisis cast a shadow of uncertainty — on the Korean Peninsula and the rest of the world.

But fast forward 10 months, and the shaky state of affairs has flipped: Trump and Kim are expected to attend a historic summit Tuesday in Singapore in the first meeting between a sitting U.S. president and a North Korean leader.

It's a face-to-face that few might have thought possible after the insults traded, but one that observers say could signal the start of meaningful denuclearization on the peninsula, normalized relations between the two countries and the two Koreas, or even a step toward lasting peace and security.

How did the U.S. and North Korea get to this point?

Nearly a month after Trump took office in January 2017, North Korea flashed its first show of defiance toward the new U.S. administration by launching a solid-fueled ballistic missile from a submarine.

It led to further tests and, eventually, to the U.S. responding by sending an aircraft carrier to the region and the U.N. Security Council approving tougher sanctions against the North because of its weapons program.

Last year was also marked by events that hampered already strained relations: American college student Otto Warmbier, who was imprisoned in North Korea for 17 months, died after his unexpected release, and Trump, during an address of the U.N. General Assembly, belittled Kim as a "rocket man."

But while the two countries appeared to be on the brink of a nuclear showdown, a shift occurred in February with the Winter Olympics in South Korea, when North and South marched together under a unified flag. The two countries, which have technically been at war since 1953, later agreed to restart a dialogue.

Then, in March, came a surprise announcement: The United States and North Korea said Trump and Kim would meet this spring — inspiring both hope and trepidation in the region.

The U.S. and the North have no formal diplomatic channels. Never before have heads of state from each country held talks, although former president Jimmy Carter met with North Korea's founder, Kim Il Sung, and former president Bill Clinton met with Kim Jong Il, the son of Kim Il Sung and father of Kim Jong Un, after they had respectively left the White House.