One of the stranger features of Germany's political landscape is the existence of the Christian Social Union (CSU), a separate center-right party in Bavaria that sometimes complements, sometimes rivals, and sometimes just runs parallel to the main nationwide conservative party, the Christian Democratic Union (CDU).

The two parties, which together have dominated German politics in the post-war era, are bound by a deal that means they are fused together and yet separate: In exchange for not competing in each other's territories, the two parties agree to form a nationwide force at the federal level, even though they have separate organizational structures and leadership, run separate party conferences, and have separate programs.

In effect, that means that the CSU is a regional party that wields national power. Though the CSU only fields candidates in Bavaria, it has representatives in the federal parliament, the Bundestag, as part of the joint CDU/CSU parliamentary group. And, if the CDU/CSU wins a national election, the Bavarian party is guaranteed seats in the Cabinet — where it traditionally runs the Transport and Agriculture ministries, among others. Bavaria's strong automobile industry and its agricultural traditions are key to its identity.

The marriage, though mutually beneficial, has not always been easy. In 2015 and 2016, CSU Interior Minister Horst Seehofer clashed bitterly with Chancellor Angela Merkel over her migration policy, and the resulting crisis almost brought down her government.

Then, in the run-up to 2021, the two parties virtually came to blows over which of them should get to field the national chancellor candidate after Merkel's retirement. More recently, however, the party leaders Friedrich Merz (CDU) and Markus Söder (CSU) have been getting on noticeably well — better, in fact, than many expected, seeing as the two are considered highly ambitious and might have legitimate claims for the chancellor candidacy in 2025.

A historic alliance

The CSU was founded in October 1945, immediately after the end of World War II, at a time when, as Germany was essentially starting its political system from scratch, new conservative parties and associations were coalescing all over the country. But, whereas the other local conservative parties joined together in 1950 to form the CDU, the CSU chose to retain its independence.

That was in part because there had traditionally been at least one Bavarian regional interest party in German national politics. The CSU fit this mold and still wears its Bavarian patriotism on its sleeve today, and, after dispatching a couple of rival Bavarian parties in the 1950s, it established itself as the dominant force in southeastern Germany.

For much of its history, particularly from the late 1960s to the 1990s, the CSU consistently won more than 50% of votes in both federal and state elections in Bavaria, which became the only German state with a one-party government. More often than not, the CSU leader has also been Bavaria's state premier.

But the party's vote has splintered in recent years: Other right-wing rivals, like populist center-right Free Voters and the far-right Alternative for Germany (AfD), have gradually peeled off sections of its electorate.

Where CSU and CDU differ

The CSU is traditionally considered more socially conservative than the CDU, especially on religion and law enforcement: It still takes Bavaria's Catholic traditions seriously: In 2018, Markus Söder ordered that all public buildings hang a cross up prominently "as an expression of Bavaria's historical and cultural character." The Bavarian state police have also been much tougher on public order, and the state is visibly clamping down more ruthlessly on climate protesters than in other states.

But at the same time, the CSU is often to the left of the CDU on social welfare issues, albeit with a view to preserving what it sees as traditional family structures. In the past, it has demanded that the state do more to assist stay-at-home mothers.

The party's stance on non-Germans, however, is less generous. The CSU took a much tougher line on rejected asylum seekers during the Merkel government.

The CSU's nationalism also led the country into one of its embarrassing debacles in 2019, when the European Court of Justice ruled that a CSU plan to introduce a toll on foreign cars on the highway was deemed against European Union rules. That left the federal government facing the loss of €243 million ($267 million) for contracts that CSU Federal Transport Minister Andreas Scheuer had signed. A legal battle is ongoing.

CSU national aspirations to lead

On just two occasions, the CDU/CSU has put forward a CSU candidate for chancellor in national elections. Franz-Josef Strauss, a godfather-like figure in the party, ran in 1980, and Edmund Stoiber — after a tussle with then CDU leader Angela Merkel — threw his hat in the ring in 2002.

Neither was successful. Strauss was extremely conservative and failed in a bid to unseat incumbent Helmut Schmidt from the center-left Social Democrats (SPD); Stoiber failed to appeal to voters in northern Germany and lost a narrow contest to Chancellor Gerhard Schröder.

Schröder famously tried to claim election victory in 2005 by arguing that ballots for the CDU and CSU should be counted separately. That would have meant that Schröder's Social Democrats (SPD) secured the most votes — and the mandate to form a new government.

Few people bought that line of reasoning. The majority of Germans most of the time see the CDU/CSU as a single political entity, despite their occasional wrangles.

This is an updated version of an earlier article. Jefferson Chase contributed to this article.

Edited by: Rina Goldenberg

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