Nikel brings more than four decades of experience in the German Foreign Office to the discussion. Over the course of his career, he served in postings including Moscow, Nairobi, Paris and Washington, D.C., and led the German embassy in Warsaw from 2014 to 2020. He was also involved in the preparations for the 2015 Iran nuclear agreement (JCPOA), an experience that appears to underpin his enduring commitment to negotiated, verification-based disarmament as the more durable alternative to military coercion. Since 2020, he has served as Vice President of the DGAP, one of Germany's leading foreign policy think tanks. The event centred on his newly published book, Der schmale Grat: Die Kunst der Diplomatie in Zeiten des Umbruchs ("The Fine Line: The Art of Diplomacy in Times of Upheaval"), in which he reflects on the balancing acts increasingly required of foreign policy actors today.

König opened the conversation by inviting Nikel to trace his career, from his early postings through his engagement with Russia, the Balkans, Poland and the Iran nuclear negotiations. From there, the discussion turned to the book's central argument: that as wars and international crises multiply, the effectiveness of diplomacy is increasingly called into question, a conclusion Nikel rejects. Diplomacy, he told the audience, is more essential today than at any point in recent memory, but only when paired with credible military and economic strength. That pairing, he said, had been neglected in German foreign policy for too long: "We neglected it," he admitted, calling it a mistake with lasting consequences.

The title of the book refers to the narrow path diplomats must walk between competing imperatives. Nikel illustrated this with the war in Ukraine, where Germany and its allies must balance support for Ukraine's defence against the risk of a broader confrontation between Russia and NATO. A second example he raised was the tension between upholding a multilateral, rules-based international order and simultaneously building pragmatic partnerships with countries in Africa and Latin America. Here, he drew a firm distinction between alliances, which he characterised as resting on shared values and a common worldview, and partnerships, which he described as oriented more toward economic and trade interests.

Reflecting on Germany's post-Cold War relationship with Russia, Nikel called it a failure, attributing it partly to Berlin's preoccupation with the Balkans during the 1990s. When König asked him directly whether he bore personal responsibility for the shortcomings of that policy, Nikel answered candidly in the affirmative, saying that warning signs, including the wars in Georgia and the annexation of Crimea, were not adequately heeded at the time. "We did not see the writing on the wall," he commented. Nikel linked this to a broader post-Cold War assumption that Europe had entered a new era of lasting stability, an optimism he associated with Kant's "social contract" vision of international relations that did not survive subsequent events.

On the Middle East, Nikel described Israel's military response in Iran as a strategic failure, disproportionate to the aims it sought to achieve, while acknowledging that Israel's wish to defend itself after the October 7 attacks was understandable. He argued that the 2015 Iran nuclear deal (JCPOA) had done considerably more to contain Iran's nuclear ambitions than the current approach is likely to achieve, offering a blunt assessment: "You cannot bomb the knowledge out of their heads." Asked whether Germany's approach to the Israel-Gaza conflict had been the right one, Nikel was critical, pointing to the German government's continued invocation of Staatsräson. The doctrine, first articulated in relation to Israel by Chancellor Angela Merkel before the Knesset in 2008, frames Israel's security as central to Germany's own reason of state. While Germany's historical responsibility toward Israel remains a legitimate foundation for the relationship, Nikel argued that this should not preclude a more critical German stance toward current Israeli policy.

Audience questions also addressed the trajectory of relations between China and Russia, with Nikel observing that Russia's war effort has depended significantly on Chinese support, even as the two countries, sometimes described as an "axis of upheaval," hold differing views on the international order. On how the West should approach Russia going forward, he set out three pillars: diplomacy, deterrence and defence. A final question on artificial intelligence prompted Nikel to note that whoever controls the technology gains a decisive advantage, while stressing that human oversight must remain in place.

Taken together, the conversation returned repeatedly to the theme at the heart of Nikel's book: that diplomacy and strength are not opposing strategies but interdependent ones, and that Germany's post-Cold War attempt to treat them as separable was its central miscalculation. From Ukraine to the Middle East to the rise of artificial intelligence, Nikel's answers suggested a consistent worldview — one sceptical of both unchecked military action and diplomacy unbacked by deterrence, and insistent that Germany's foreign policy, like the "narrow path" of his book's title, must be walked deliberately rather than drifted into. As the event drew to a close, that call for deliberateness, more than any single policy prescription, appeared to be Nikel's principal message to the audience gathered at the Waldorf Astoria.

• Independent