BERLIN – As someone who was born in 1948, the risk of a nuclear World War III was a very real part of my childhood. That threat – or at least the threat of East and West Germany both being completely destroyed – persisted until the end of Cold War and the collapse of the Soviet Union.

Since then, the risk of nuclear-armed superpowers triggering Armageddon has been substantially reduced, even if it has not disappeared entirely. Today, the bigger danger is that an increasing number of smaller countries ruled by unstable or dictatorial regimes will try to acquire nuclear weapons. By becoming a nuclear power, such regimes can ensure their own survival, promote their local or regional geopolitical interests, and even pursue an expansionist agenda.

In this new environment, the "rationality of deterrence” maintained by the United States and the Soviet Union during the Cold War has eroded. Now, if nuclear proliferation increases, the threshold for using nuclear weapons will likely fall.

As the current situation in North Korea shows, the nuclearization of East Asia or the Persian Gulf could pose a direct threat to world peace. Consider the recent rhetorical confrontation between North Korean dictator Kim Jong-un and US President Donald Trump, in which Trump promised to respond with "fire and fury” to any further North Korean provocations. Clearly, Trump is not relying on the rationality of deterrence, as one would have expected from the leader of the last remaining superpower. Instead, he has given his emotions free rein.

Of course, Trump didn’t start the escalating crisis on the Korean Peninsula. It has been festering for some time, owing to the North Korean regime’s willingness to pay any price to become a nuclear power, which it sees as a way to ensure its own safety. In addition, the regime is developing intercontinental ballistic missiles capable of carrying a nuclear warhead and reaching the West Coast of the US, or farther. This would be a major security challenge for any US administration.

Ultimately, there are no good options for responding to the North Korean threat. A US-led pre-emptive war on the Korean Peninsula, for example, could lead to a direct confrontation with China and the destruction of South Korea, and would have unforeseeable implications for Japan. And, because the China-South Korea-Japan triangle has become the new power center of the twenty-first-century global economy, no country would be spared from the economic fallout. Even if the US continues to allude to the possibility of war, American military leaders know that the use of military force is not really a viable option, given its prohibitively high costs and risks.

When North Korea achieves nuclear-power status, the American security guarantee will no longer be airtight. A North Korea with nuclear weapons and the means to use them would add pressure on South Korea and Japan to develop their own nuclear capacity, which they could easily do. But that is the last thing that China wants.

The situation in Asia today has the nuclear attributes of the twentieth century and the national-power dynamics of the nineteenth century. That could prove to be a highly inflammatory cocktail. And at the same time, the international system is becoming increasingly unstable, with political structures, institutions, and alliances around the world being upended or called into question.

Much will depend on what happens in the US under Trump’s wayward presidency. The investigation into the Trump campaign’s possible collusion with Russia ahead of the 2016 presidential election, and the failure to repeal the Affordable Care Act (Obamacare) have shown the US administration to be unstable and ineffective. And agenda items such as tax cuts, the Mexican border wall, and the renegotiation of the North American Free Trade Agreement – to say nothing of Trump’s own emotional outbursts – are fueling America’s radical right.

Instability within the US is cause for global concern. If the US can no longer be counted on to ensure world peace and stability, then no country can. We will be left with a leadership vacuum, and nowhere is this more dangerous than with respect to nuclear proliferation.

Another nuclear danger looms this fall. If the US Congress imposes new sanctions on Iran, the nuclear agreement between that country and the P5+1 (the five permanent members of the United Nations Security Council, plus Germany) could fail. Iranian President Hassan Rouhani publicly announced just last week that Iran could abandon the deal "within hours” in response to new sanctions.

In light of the North Korea crisis, it would be the height of irresponsibility to trigger a gratuitous nuclear crisis – and possibly a war – in the Middle East. And a return by the US to a strategy of regime change in Iran would likely be self-defeating, because it would strengthen the country’s hardliners.

All of this would be taking place in a region that is already riven by crises and wars. And, because Russia, China, and the Europeans would stick to the nuclear deal, the US would find itself alone and at odds with even its closest allies.

Today’s nuclear threats demand exactly the opposite of "fire and fury.” What is needed is level-headedness, rationality, and patient diplomacy that is not based on dangerous and fanciful threats of force. If the last superpower abandons these virtues, the world – all of us – will have to confront the consequences.

Joschka Fischer, Germany’s foreign minister and vice chancellor from 1998 to 2005, was a leader of the German Green Party for almost 20 years.

Copyright: Project Syndicate.