Europe Day, 9 May, was a symbolic date chosen for signing a bilateral treaty between France and Poland. And so was the venue: in the mid-18th century, Nancy was the residence of the Polish King Stanislas Leszczynski, who later became Duke of Lorraine, having been exiled from his country, and whose daughter, having married Louis XV, become Queen of France.
Fit for a New Age
The treaty reflects the long shared history between France and Poland, even if this was less apparent in the 20th century, particularly after 1939. More recently, however, relations have become complicated due to, in particular, a strong Atlanticist stance in Warsaw. This led to points of tension in defence: for example, Poland’s participation in the Iraq War in 2003, as well as its preference for the F-16 over the Mirage-2000 the same year and for the UH-60 Black Hawk helicopter over the Caracal in 2016. Russia’s war in Ukraine and Poland’s growing role in supporting Kyiv led to a warming of relations under the PiS government. The trend continued and intensified in 2023 with the return to power of the pro-European Prime Minister Donald Tusk, whose ideas are often in line with those of the French President Emmanuel Macron.
The treaty serves as a further illustration of France’s pivot towards the east, alongside its greater involvement in NATO, including through its military deployments in Estonia and Romania. Emmanuel Macron acknowledged, in his Globsec Summit’s speech in Bratislava in June 2023, France’s failure to listen and ignoring of the warnings from central and north-eastern European countries about the Russian threat. The French President confirmed this idea at the press conference in Nancy: he recalled the dark times (the 1930s, the Cold War, and misunderstandings of recent years, particularly concerning the Russian threat) but marked the opening of a new era between the two states and greater alignment on European security objectives.
Bilateral Defence Relations
Poland and France inked a treaty in 1991, but the previous version was far less structured than the one signed on 9 May. The new ‘Treaty for enhanced cooperation and friendship between the Republic of Poland and the French Republic’, known as the ‘Nancy treaty’, places Poland among France’s closest European partners. Indeed, France shares this type of agreement with a small group of countries: Germany via the Elysée (1963) and Aachen (2019) treaties, Italy via the Quirinale Treaty (2021), and Spain via the Barcelona Treaty (2023). The United Kingdom (Lancaster House Treaty in 2010) and Greece (strategic partnership in 2021), too, have major defence agreements with France. All countries in the E5 format (i.e., France, Germany, Italy, Poland, and the UK), a grouping preferred for defence meetings in recent months, now have an exclusive agreement with France.
The treaty covers a wide range of issues: from economy and climate change to energy, with a large section devoted to nuclear energy (a cooperation plan in this area has been signed alongside the treaty), as well as agriculture and immigration. But it is the defence section that stands out, in particular, due to the defence and mutual assistance clause. Article 4 (Paragraph 2) reproduces the guarantees of Article 5 of the North Atlantic Treaty and Article 42.7 of the EU Treaty: “In accordance with the provisions of Article 51 of the Charter of the United Nations, in case of armed attack against their territory, the Parties shall assist each other, including with military means. This aid and assistance will be implemented in accordance with commitments stemming from the Article 5 of the North Atlantic Treaty and paragraph 7 of Article 42 of the Treaty on European Union.” This wording is more detailed than the equivalent clauses in the Quirinale and Barcelona treaties and seems closer to those of the treaties with the United Kingdom, Germany, and Greece.
These French bilateral defence clauses seem to differ depending on the level of partnership. The Lancaster House Treaty is the only treaty in which vital interests are mentioned, considering that the UK and France are nuclear powers, while the Aachen treaty refers to the inextricably linked security interests of France and Germany, building on history and direct neighbourhood. They also differ by the recognition of the level of the threat (particularly for Greece; much less so for Spain and Italy, where there is no assessment of a real immediate threat, except terrorism). The Polish assistance clause is a signal of France’s strengthened solidarity towards a partner in central Europe, where the Russian threat is more acute due to the shared border.
A European Dimension of French Nuclear Deterrent
Nuclear deterrence as such does not appear in the Nancy treaty. However, in response to questioning during the press conference, the French President stated that all components were included. He pointed out that strategic ambiguity had been at the heart of French doctrine since the 1960s and was key to the nuclear deterrent’s effectiveness. As for the European dimension of French nuclear deterrent, this was already present under President Charles de Gaulle—notably with West Germany in mind at the time—and reaffirmed by all his successors. Hence, for Emmanuel Macron, “in deciding what vital interests are, the interests of our main partners are taken into account.”
The French President thus continued the discussion that he had opened with his nuclear doctrine speech on 7 February 2020. At that time, he indicated the willingness to engage in a strategic dialogue “on the role played by France’s nuclear deterrence in the collective security” with the European partners who would be “ready for it.” In that speech, he specified that the Europeans “could be associated with the exercises of French deterrence forces” if they wanted to. Macron then went a step further when, in an interview with French media on 13 May 2025, he was asked about recent statements by Poland and Germany who wished to engage France on nuclear deterrence issues. Macron replied that he was ready to open discussions, albeit with some caveats: “Paris would not pay for the security of other countries; any deployment of France’s nuclear weapons could not deplete its ability to defend itself; and any decision to use the bomb would remain solely in the hands of the French President.”
The European Preference
The other significant element in the Franco-Polish agreement is the emphasis given to European defence, which can be seen as a major shift on the part of Warsaw. While the role of the transatlantic relationship in the European security architecture is recognised in the first paragraph of Article 4, the importance of developing a “stronger and more operational European defence” in order to “assume greater responsibility for its own defence” is mentioned as well. The strengthening of the European defence industry is also underlined: Article 4.9 states that “European preference” should be “progressively promoted,” a point that appeared to be a French priority and was reiterated at the press conference by the Polish prime minister. This may well suggest that Poland could push for a strong European preference in order to speed up the adoption of EDIP at the end of its presidency of the Council of the EU next June.
Joint work in countering hybrid and information threats, as well as in strengthening military mobility appear articles 4.8 and 4.12. References to military mobility resurface in Article 4.16 and in the transport section of Article 8.2. The efforts to bring forces closer together to ensure preparedness and interoperability between the two countries will be implemented through joint exercises (Article 4.15).
A treaty for European security
The Nancy treaty is now part of a network of bilateral treaties and privileged discussion formats, including the Weimar Triangle. Relaunched in 2024, the latter is now key to European politics: the day after his election as chancellor, Friedrich Merz visited France and Poland, demonstrating the importance of central Europe on the European stage today. This format was also reiterated in the introductory remarks of the Polish prime minister at the Nancy press conference. The four leaders of France, Germany, Poland, and the UK were together in Kyiv on 10 May, attending a meeting of the coalition of the willing in Ukraine.
These bilateral and multi-bilateral formats aim to promote the development of a common strategic culture. The latter is mentioned in Article 4.4 of the Nancy treaty: “The Parties shall seek to create a shared strategic culture and to establish shared positions on issues affecting their security and defence interests.” It will be implemented through regular strategic dialogues, including at the level of foreign affairs and defence ministers.
The Nancy treaty comes at a time when the transatlantic relationship has been undermined by brutal invective on European security coming from the US. The agreement between France and Poland is a clear signal that Europeans are taking control of their own defence, thus contributing to a stronger “European pillar” within NATO: this very expression is used in Article 2.2. In their remarks at the press conference, the two leaders reaffirmed that the goal was to be better Allies within the Alliance—as desired by Washington—notably by developing European capabilities through investment and increased defence spending.
Views expressed in ICDS publications are those of the author(s).