As North Korea drives towards creating a nuclear-tipped missile capable of hitting mainland America, joint US-South Korea military exercises are an annual source of tension
Geopolitical tensions flare every spring on the Korean peninsula, but analysts say the anxiety of recent weeks has been magnified by the unpredictable new player in the annual drama: Donald Trump.
North Korea always intensifies its rhetoric when Seoul and Washington stage annual large-scale joint military drills that it condemns as rehearsals for a potential invasion.
But this time threat and counter-threat from both sides sent tensions spiralling, generating lurid headlines and focussing global attention on the region.
The North says it needs nuclear weapons to protect itself and observers agree it is making progress towards a long-dreamed-of rocket capable of delivering a warhead to the US mainland.
With multiple sets of UN sanctions failing to quell its ambitions, Secretary of State Rex Tillerson last month said US military action was an "option on the table".
Pyongyang promised "the toughest counteraction" to any attack while Washington pledged an "overwhelming response", with Trump himself tweeting that the North "will be taken care of".
Even so the North has carried out two rocket tests this month alone and paraded its arsenal, including a suspected new intercontinental ballistic missile (ICBM), through the streets of Pyongyang.
Speculation has also mounted that it could carry out a sixth nuclear test, following two last year, although that has yet to happen.
Pyongyang's threats and actions are not unusual -- it has gone further in the past, sinking the South Korean corvette Cheonan with the loss of 46 lives in 2010, and three years later urging foreigners to leave the South to escape what it said was a looming nuclear war.
But cooler heads always prevailed in Washington and the two sides never came to blows. Analysts now point to the new US administration as a key factor behind the intense fears of conflict this time.
"The big change was from Washington," said Koo Kab-Woo, professor at the University of North Korean Studies in Seoul.
After years of "strategic patience" under Barack Obama, he said the US is "reacting more sensitively" to claims by leader Kim Jong-Un Kim that his country is in the final stages of developing an ICBM.
- 'Turning It Up to Eleven' -
A missile strike in Syria and the dropping of the "Mother of All Bombs" in Afghanistan sent ominous signals that the new administration is prepared to unleash US firepower.
And after a summit with Chinese President Xi Jinping, Trump doubled down on a vow to act unilaterally against Pyongyang if Beijing fails to rein in its unpredictable ally.
"The ascendancy of Donald Trump introduces a greater element of uncertainty about America's moves," said Mark Fitzpatrick, executive director at the International Institute of Strategic Studies in Washington.
"His threatening tweets make people wonder whether he would also attack North Korea," he told AFP.
The North itself is already renowned for belligerent statements.
Mason Richey of Hankuk University of Foreign Affairs in Seoul described its propaganda as "ranging from insulting to bellicose to ludicrous" in a recent paper titled "Turning It Up to Eleven" -- a rare reference in diplomatic analysis to the 1984 rock mockumentary "This Is Spinal Tap".
But he found no correlation between the North's verbal hostility and its actual actions.
"US civilian and military decision-makers should greatly discount North Korea's threat rhetoric" unless it is accompanied by other signals, he said.
- 'Commitment trap' -
Analysts say Trump's tweets -- which often use unrefined and harsh rhetoric -- and his unpredictability have also unsettled Beijing.
"Both China and North Korea are stunned by Washington's change," said Choi Kang, an analyst at the Asan Institute for Policy Studies.
But the US has yet to translate words into action and its misstep over the deployment of a naval strike group to the Korean peninsula, which turned out to be thousands of kilometres away, has caused embarrassment.
Questions have been raised whether Washington's statements will create a "commitment trap" where it feels obliged to act to maintain its credibility.
"It can be hard to distinguish bluff from real intentions, and President Trump is a master at keeping the other side guessing," said Fitzpatrick.
But the commander-in-chief "does not seem to care much about following through on past promises", he added. "He is infinitely flexible in his policy choices."