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French President Emmanuel Macron and Polish Prime Minister Donald Tusk met in the historic eastern French city of Nancy on May 9, 2025, to sign a historic strategic defense cooperation treaty.

The agreement marks a new era in Franco-Polish relations, placing mutual security guarantees at its core and reinforcing the European Union’s defense posture in the face of mounting threats from Russia.

“For me, absolutely the most important issue was the mutual security guarantees,” said Tusk, speaking to reporters before traveling to France. “The very essence of this treaty,” he emphasized, is the mutual support provision.”

The treaty outlines that in the case of an attack on either Poland or France, both nations commit to provide mutual assistance, including military support. While the specifics of such assistance remain undisclosed, Tusk hinted at a broader scope of defense cooperation, including potentially tapping into France’s nuclear umbrella. “The treaty also opens up the possibility of cooperation in that area,” he said, about France’s nuclear deterrent.

The signing comes at a moment of heightened anxiety across Europe, with the war in Ukraine entering its third year and uncertainty growing over NATO’s future role under the potential return of former U.S. President Donald Trump. Trump’s previous comments urging Europe to take more responsibility for its defense have added urgency to intra-European military cooperation efforts.

New era of European defense

“This treaty will lift the Franco-Polish partnership to a high level of ambition in strategic areas for our two countries and Europe, particularly defense and energy,” announced the French presidency ahead of the signing.

It also reflects the recalibration of European defense leadership, with Germany’s internal political instability providing an opening for Poland to assume a more prominent role.

The Franco-Polish alliance sends a clear message of European solidarity at a time when Russia showcased its own geopolitical muscle. On the same day, President Vladimir Putin presided over the Victory Day military parade in Moscow’s Red Square, with Chinese President Xi Jinping in attendance, a visible reminder of the shifting global alliances and the growing Moscow-Beijing axis.

Poland’s military ambitions and regional role

Poland has rapidly emerged as a defense heavyweight in Europe. According to NATO data, the Polish army is set to field 216,000 troops in 2025, surpassing both France’s 205,000 and Germany’s 186,000. Warsaw has ambitious plans to increase its forces to 300,000 by 2035, which would make it the largest army within the European Union.

Such a move also makes strategic sense for Poland, which shares a tense eastern border with the Russian exclave of Kaliningrad and has frequently raised alarms over possible Russian aggression. France, as the EU’s sole nuclear power, represents a crucial deterrent partner for Poland in this volatile context.

Implications on Poland’s domestic politics

Tusk has called the treaty both “historic” and a “game-changer” for Europe. It also symbolizes a political transformation in Warsaw. Since returning to power in late 2023, Tusk has sought to realign Poland more closely with its European allies, undoing years of estrangement under the previous nationalist Law and Justice (PiS) government.

The timing of the agreement is politically charged as well. Poland is heading into a critical presidential election on May 18, where the pro-European camp supported by Tusk faces a stiff challenge from a nationalist candidate backed by PiS. Analysts warn that Russia could exploit the moment through disinformation campaigns, as it has in previous European elections.

Toward a new European security order

Macron, for his part, has floated the idea of extending France’s nuclear deterrent to other EU states, a concept that now seems less abstract and more feasible in light of the new treaty. The agreement with Poland could become a model for deeper bilateral or multilateral defense agreements within the EU, particularly if American support for NATO continues to fluctuate with U.S. political cycles.

As Russia continues to destabilize the region and the United States questions its long-standing commitments, Europe’s own defense architecture is undergoing a quiet revolution. The Franco-Polish treaty is a significant milestone in that transformation, one that could shape the continent’s security dynamics for decades to come.

En route pour Kyiv.
Pour l’Ukraine, pour l’Europe.

On our way to Kyiv.
For Ukraine, for Europe.

Auf dem Weg nach Kyjiw.
Für die Ukraine, für Europa.

W drodze do Kijowa.
Dla Ukrainy, dla Europy. pic.twitter.com/a6zxOYRR0B

— Emmanuel Macron (@EmmanuelMacron) May 9, 2025