As a journalist, I have always dreaded reporting on meetings between world leaders billed as “historic” or “momentous” or just plain “significant”. Such pretensions are usually phoney or, even if something of interest really does happen, its importance is exaggerated or oversimplified.

But plus ca change is not always a safe slogan for the cautious reporter, because real change does occasionally take place and professional cynics are caught on the hop.

Watching the “historic” meeting between the leaders of North and South Korea at the Panmunjom border crossing this weekend – and listening to reporters bubbling over with excitement – it was difficult not to be captured by the enthusiastic mood.

But I recall similar meetings that were once billed as transforming the world for the better and are now largely forgotten. How many people remember the Reykjavik summit between Reagan and Gorbachev in 1986, which once seemed so important? Then there was the famous handshake on the lawn of the White House between Israeli prime minister Yitzhak Rabin and Palestinian leader Yasser Arafat confirming a peace deal between Israel and the Palestinians in 1993 that, whatever else happened, did not produce peace.

Rabin was assassinated two years later by a religious fanatic and Arafat died with his hopes for Palestinian self-determination in ruins. Sceptics who had argued that disparity in political and military strength between Israel and the Palestinians was too great for a real accord turned out to be right.

The meeting in Panmunjom feels as if it has got more substance, primarily because the balance of power between the two sides is more even: Kim has nuclear weapons and claims to have a ballistic missile which could reach the US. Their range and reliability may be exaggerated but nobody wants to find out the hard way. It is these intercontinental ballistic missiles which make Washington and the rest of the world take North Korea seriously as a state, though otherwise it is an insignificant, economically primitive, family dictatorship. Despite Kim’s pledge that he is seeking a denuclearised Korean peninsula, this is the last thing that is going to happen because he would be foolish to give up his only serious negotiating card. North Korea has a long track record of dangling nuclear concessions in front of its enemies only to snatch them back later.

This does not mean that serious things are not happening. Relations between North and South Korea are being normalised symbolically and, to a degree yet to be seen, in practice. There is to be a formal end to the Korean War replacing the 1953 armistice, an end to “hostile activities” between the two states, family reunification, road and rail links and joint sporting activities. Ritualistic propaganda broadcasts across the Demilitarised Zone (DMZ) are to cease, though it would be interesting to know if they are also going to remove the minefields in the DMZ.

President Trump is claiming that it was his bellicose tweeting and harsh sanctions that forced Kim to negotiate. Maybe they had some impact, but there are limits to what sanctions can achieve against a dictator firmly in power (witness UN sanctions on Saddam Hussein’s Iraq between 1990 and 2003). Trump’s threats of “fire and fury” may or may not frighten the North Korean leader, but they certainly make US allies nervous and less willing to let their fate be unilaterally determined by an unpredictable and dysfunctional administration in Washington.

Compare the de-escalating crisis over North Korea’s nuclear weapons with the escalating one over the 2015 Iran nuclear deal from which Trump is likely to withdraw the US on 12 May. This brings us to the second international meeting this week, this time between Trump and French president Emmanuel Macron in Washington, which had plenty of artificial-sounding bonhomie, but not much else.

It was the worst type of state visit in which governments and the media are complicit in pretending that there is real amity and agreement. Kisses and handshakes were exchanged, and pictures of Trump removing a speck of dandruff from Macron’s jacket were beamed across the planet, as if they signified anything. Once commentators would use the sugary phrase “personal chemistry” to describe a non-existent warmth between leaders, though this is being replaced by “personal rapport” which is a little less offensive.

Strong emotional bonds between Trump and other human beings seem unlikely to me, given his manic self-obsession. He resembles an eighteenth century monarch presiding over a court in which there is an ever-changing array of courtiers, who are powerful one day only to be abruptly dismissed the next.

Some US commentators have found reasons why the two men should get along. I particularly like a tweet by “The Discourse Lover”, who writes sarcastically: “I actually bet Trump and Macron get along great – Trump is the exact type of vulgar, acquisitive simpleton that French people assume all Americans are, Macron is the exact type of preening, arrogant creep that Americans assume all French people are.”

Macron did not have any illusions that his “personal rapport” was getting him anywhere when it came to Iran. He confirmed that Trump will most likely kill the Iran nuclear deal “for domestic reasons” and will impose “very tough sanctions” on Iran. Angela Merkel is in Washington today and will see Trump, but is equally unlikely to change his position on Iran or anything else.

The Iran crisis is truly dangerous in a way that was never quite true of the North Korea crisis. In Korea, we are talking of a peace agreement that would replace the Panmunjom Armistice of 1953, but there has been no war going on there for 65 years, though there have been a few sporadic clashes. Compare this with the position of Iran which is a rival for influence with the US in a ferocious war in Syria and one that in Iraq that is currently receding, but could easily blaze up again.

The crisis in relations between the US and Iran has been going on so long – essentially since the fall of the Shah in 1979 – that people may be self-immunised against reacting to its latest and most dangerous phase. Trump will be withdrawing from an agreement with which all signatories – US, UK, France, Germany, Russia and China – agree that Iran is in compliance. The US will reimpose sanctions, which will be damaging to Iran, but not be as painful as those imposed before the 2015 deal, because this time round they will have much less international support.

Iran will inevitably resume all or part of the nuclear programme halted by the 2015 agreement since it will no longer receive any benefit from it. Trump may want a tougher deal but his own arbitrary actions have reduced the US diplomatic and economic leverage which he would need to obtain one. The Iranian leadership may respond cautiously to Trump’s demarche in order to isolate the US and draw out a crisis that weakens the Americans more than it does the Iranians.

Short of diplomatic options, the White House might view military action against Iran as an increasingly attractive approach. The Iran and North Korea crises are very different but in both cases Trump is behaving as if the US is turning into a stronger power when, thanks to his leadership, it is becoming a weaker one.