Could the U.S. start a nuclear war?

WASHINGTON — U.S. president Donald Trump said on Wednesday that the U.S. nuclear arsenal is "far stronger and more power than ever before" after warning North Korea that their provocations would be met with "fire and fury" the previous day.

The U.S. Constitution gives Congress the power to declare wars and authorize funds to support them. The president would normally appeal to Congress for authorization if he wants to declare wars.

However, the president also has temporary authority for 60 days to use force without congressional approval. Even though the decision cannot be opposed, Congress can choose to cut funding if it believes the military engagement is not in the best interest of the country.

Under international law, the U.S. may only use military force against another sovereign state if it faces an imminent, unprovoked and certain threat. The U.S. may use force in anticipation of that imminent attack but it cannot declare war based on potential threats.

Or, the U.S. could declare wars after receiving an authorization from the UN Security Council, which it serves as a permanent member. However, other permanent members such as China and Russia could veto the appeal.

"Any decision that the president were to take now, or that he took in January, would take years to implement," Jon Wolfsthal, who served in the Obama administration as the National Security Council's senior director for nonproliferation and arms control told the Washington Post. "I'm very skeptical of the idea that Trump believes that he has modernized or adjusted our arsenal, because there have been no visible changes to it."

On the other hand, countries in Asia are having mixed feelings towards President Trump's recent language.

"Trump doesn't seem to understand what an alliance is, and doesn't seem to consider his ally when he says those things," Lee Byong-chul, a senior fellow at the Institute for Peace and Cooperation in Seoul told the New York Times. "No American president has mentioned a military option so easily, so offhandedly as he has. He unnerves people in South Korea, few of whom want war in Korea."

The U.S. and North Korea came very close to war in 1994 after Pyongyang announced its intention to withdraw from the Nuclear Non-Proliferation Treaty. The crisis was reportedly resolved after a top-level diplomatic meeting of former U.S. president Jimmy Carter and former DPRK leader Kim II Sung.