How a Dutch merger just cost the European Greens a founding party

On 25 September, the members of the new Dutch party ‘Progressief Nederland’ (PRO), founded as a merger between GroenLinks (the Dutch Greens) and the Social Democrats, decided in a party ballot join the Party of European Socialists (PES). Progressief Nederland’s choice cost the European Greens one of their founding parties. The merger was initially embraced as an example of further collaboration between the Greens and PES, but it ended chaotically, with both European parties campaigning to win PRO. This puts future collaboration under pressure and shows the limits of the European party system.

The Dutch party system saw a big reshuffle on its progressive side this summer. GroenLinks and the Labour Party (PvdA) merged into Progressief Nederland (PRO) on 1 July 2026, formalising a cooperation that already existed in practice. The aim was to end fragmentation on the left and build a large left bloc with the weight to compete for governing power. This decision was backed by research that projected a merged party at around 37 seats, more than one plus one. So far, that promise has not been delivered: after 25 seats on a joint list in 2023, the combination fell back to 20 in 2025.

The same logic of power shaped PRO’s European strategy. After long delaying the decision of which family to join in the European Parliament, the party board handed the issue to an advisory committee. They concluded that a national party cannot be a full member of two European families, and as member parties had to be reported to the Authority for European Political Parties by 30 September 2026, a party ballot before this date was needed. The committee advised full membership of the PES, citing the family’s presence in the Commission and among heads of government and ministers in the Council, measuring influence based on who is currently occupying executive posts.

The forced choice opened a rift in an already politically tense merger that was meant to showcase cooperation on the left. What could have been a strategically thought-out step turned into a painful fight, with members campaigning for the family they felt they belonged to. The European families did not stand aside. The European Green Party co-chair and Greens/European Free Alliance co-president showed party support at a Green event in Amsterdam a week before the vote.

The limits of the European party system

On 25 September, the members of the new Dutch party ‘Progressief Nederland’ (PRO), founded as a merger between GroenLinks (the Dutch Greens) and the Social Democrats, decided in a party ballot join the Party of European Socialists (PES). Progressief Nederland’s choice cost the European Greens one of their founding parties. The merger was initially embraced as an example of further collaboration between the Greens and PES, but it ended chaotically, with both European parties campaigning to win PRO. This puts future collaboration under pressure and shows the limits of the European party system.

In many member states, the strategy of centre-left forces joining up across family lines to keep the far right out of power has been proven to work. In Sweden, the Social Democrats, the Left Party, the Greens and the Centre Party won a narrow majority as a bloc on 13 September. But as national party landscapes are being reshaped, the European parties are falling behind.

The left European parties remain strictly organised around fixed families. According to the regulations of the Authority for European Political Parties, membership must be genuine, with full rights in internal governance and regular fees; anything looser, such as observer or partner status, does not count. A merged red–green party can therefore only be fully at home in one family. The outcome of the party ballot promises the strongest possible link with the Greens, but what this means is still unclear. A question that should have been clarified before the ballot and the advice of the committee. After a contest in which both families took sides, it is a promise that may be hard to operationalise, contributing to a painful split.

That a decision had to be made was already clear for the European parties in 2025. This case could have been an opportunity to explore together how this merger could work and what the ‘strongest possible link’ with the second party could be. Instead, the Dutch case shows the limitations of the European parties adapting and leveraging these national opportunities and ended in a public disagreement splitting the new party in two camps and pushing the European parties further apart. This is consequential in times of the European People’s Party’s increased cooperation with the Venezuela coalition. Their incapacity to collaborate and form a bloc should be a concern for both the PES and Green party.

For the European Greens, the consequences are concrete. After 2029, the PRO delegation will sit fully with the Progressive Alliance of Socialists and Democrats. The Greens lose a founding party and a delegation that, despite its modest size, grew into a key position within the family, holding the group’s vice-presidency from 2012 and its co-presidency from 2024, with a strong record on climate, the rule of law and democracy. For the former Green members of Progressief Nederland, the move comes with uncertainty on how they can leverage their expertise after 2029. Key posts on climate, the rule of law and democracy are already held within the S&D group, often by larger national delegations with historical ties to the party.

The merger of the Dutch Greens and Social Democrats was first seen as a potential example of better collaboration on the left and of broad blocs that can deny the far right a route to government. For such pro-democratic and progressive blocs to succeed in their collaboration to gain governing power, the collaboration should also be reflected at the European level. Rather than deepening the separation between the pro-democratic progressive groups in the European Parliament, they will need to increase their collaboration. They need to create political willingness to accommodate these future hybrid alliances and parties rather than ending up in a power fight hurting established trust and collaboration. This process has shown that the binary choice will leave a bitter aftertaste for the national parties and the involved European families alike, pushing them further apart.

Liza Saris is a Project Manager and Policy Analyst at the European Policy Centre.

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