President Macron’s centrist movement En Marche, renamed La République en Marche, and Marine Le Pen’s far-right National Front, now called National Rally, misleadingly seem to have replaced the previous left-right duopoly; each commands about a quarter of the votes, but each is still a work in progress. Mr. Macron has been too busy learning and governing in the first half of his term to focus on building a proper political organization; he has been unable to widen his electoral base and has yet to define an ideological corpus beyond borrowing from both the left and the right. Lacking real party discipline, his huge parliamentary majority is showing signs of restlessness. As to Ms. Le Pen’s party, it is regaining strength but, having never won a national election, is still not seen as a governing party.

Most countries of the European Union are undergoing a similar upheaval, with varying degrees of intensity. The Brexit drama has not only driven the British mad, it has also broken their multisecular two-party system: the dominance of the Conservative and Labor parties is challenged by the far-right Brexit Party and the centrist Liberal-Democrats. Italy’s most powerful political actor is now Matteo Salvini’s far-right League, gradually sidelining its populist coalition partner, the 5-Star Movement. From afar, Germany may still look like the champion of stability, but that is an illusion: there too, two pillars, the Christian Democrats and the Social Democrats, are rapidly losing control, like agonizing dinosaurs. Have a good look at their present governing coalition, the famous “GroKo” (for Große Koalition) — it is probably the last one. Scandinavia is also experiencing fragmented majorities and awkward coalitions.

Some European countries seem to buck the trend. A closer look may provide an explanation: their political systems are inherited from their own revolutions. Spain and Portugal, whose social-democratic parties have recovered well in recent polls, didn’t come out of dictatorship until the 1970s. The same young stability applies to post-Communist Central Europe, where the left still bears the stigma of the Soviet-dominated regime and which has produced its own brand of nationalist conservatism.

If the old system is dying in the big democracies, what will replace it? Three major political forces are gathering strength in a shifting political environment where global warming and immigration are replacing traditional left-right defining issues. Nationalist right-wing parties, once marginal, are now a structural element of Europe’s political landscapes; they hold 115 of the 751 seats in the European Parliament elected last May. The center is trying to reinvent itself as a driving force; the Macron model is appealing to many young politicians outside France, but its lack, so far, of ideological mooring makes it difficult to imitate. The third and most innovative force is the Green movement. Its spectacular rise, as voters reject the traditional parties and press their leaders on the urgency to act against climate change, is mostly attributable to a mobilization of the young.

In France, the ecologist party is now the first political force among 18- to 34-year-old voters. In Germany, the well-structured Greens have jumped to 20.5 percent of the votes in the European elections; national polls now credit them with an even higher share of the vote. They are on a roll, having topped the old Social Democratic Party and even challenging Chancellor Angela Merkel’s Christian Democratic Union. The Greens’ popularity, also on the rise in the Netherlands, Belgium, Finland, Britain and Ireland, is forcing other parties to incorporate part of their agenda on environment. “No party has a monopoly over ecology any more,” claims Pascal Canfin, a French ecologist and member of the European Parliament who has joined Emmanuel Macron.