The CSU anomaly is largely the result of the highly confused and fluid politics of the immediate postwar years. Not only were politics in contention during this period, but the division of Germany into various occupation zones added a further layer of complexity. These two factors mixed so that the CSU was able to establish itself as a semi-autonomous Fraktion within the center-right CDU in the FRG.
One of the immediate problems for the postwar period was that it was not entirely clear what the future status of Germany would take. Although German division looks like an obvious inevitability in retrospect, such things were not so clear in 1946 or 1947. Some parties and their leadership entertained thoughts of a unified Germany and that the rekindled democratic party organization would transect all of Germany. The SPD's electoral paraphernalia famously showed the SPD vote traveling through the whole of Germany, including areas in the Soviet zone. The emerging CDU in the British and American zones were likewise working towards the idea o a unified Christian party that eschewed the confessional divisions of Christian democratic politics that characterized Weimar and the Kaiserreich.
Yet political support for German unity was not an automatic given in the postwar period. Regional parties also proliferated as did some champions of renewed confessionalism. Not surprisingly, Bavaria proved to be an epicenter of these centrifugal politics. Not only was this Land one of the pre-1933 strongholds of the Catholic Zentrum, but Bavaria also had one of the stronger regional identities within Germany. Bavaria fell under the purview of the American military government (OMGUS), which found Bavarian regionalist politics quite vexing. OMGUS's Bavaria chiefs found the various separatist Bavarian parties such as the Bayerische Heimat- und Königspartei (BHKP), a monarchist and particularist party, to be counterproductive to OMGUS's vision of a federal German state. The CSU was thus well primed to step into this vacuum as a party that struck a balance between Bavarian particularism and the German center-right politics necessary for the emerging Cold War. Although the CSU-OMGUS relationship was not without its frictions, especially over issues of denazification, the CSU to materialize as one of the political partners for OMGUS administration of Bavaria.
This period of bilateral military government allowed for the emergence of a number of CSU leaders that would later come to dominate the party in the early decade of the FRG. Equally important was the fact that CSU electoral successes led to the creation of a very robust party infrastructure at the local and Land level. CUS electioneering was Catholic enough to gain a solid number of former Zentrum voters, yet new and distinct enough in its platform to peel off some of the Protestant and working-class electorate. This denied not only the more separatist and right-wing parties cotes, but also the SPD. Thus Hans Erhard, the Bavaria's CSU Ministerpräsident and the Land's delegate to Länderrats (a federal council of the American zones), was able to approach the emerging German political landscape from a position of strength.
The result was that although this period of 1946-48 saw the emergence of a trans-zonal center-right party under the aegis of the CDU, the CSU did not feel the pressure to conform as did other Christian and Catholic parties. Safely in power in Festung-Bayern, CSU leaders could resist pressure to unify. The leaders of the CSU charter generation did find a good deal of common ideological ground with Adenauer's CDU, but were not about to cede their own political power. Somewhat ironically, the successes of the CSU in the occupation years paved the way for its permanent Fraktion status as the party became more sectarian on the Landtag level with Catholic conservatives like Alois Hundhammer dominating Land politics. This pushed Bavarian politics into more particularist directions such as declaring itself a Freistaat or the Landtag rejecting Basic Law.
Henry Kissinger reportedly said that Germany's tragedy was that it was too big for Europe, but too small for the world. Such an aphorism aptly fits the CSU in the postwar period. While skilled electioneering allowed it to carve out a very powerful constituency within Bavaria, the Freistaat was too small of a base to launch the CSU as a party with national reach. The CSU was a prisoner of its own success since it needed to be Catholic and Bavarian to maintain its regional hegemony and prevent it from being swallowed up by the CDU. For the most part, the early decades of the FRG meant that the symbiosis between the CDU and CSU was emeblematic of a functional relationship. The CDU government in Bonn allowed for Bavarian politicians like Franz Josef Strauß to gain national prominence. Conversely, CDU recognition of the CSU's turf in Bavaria allowed the Adenauer governments a degree of electoral security in Bundestag elections. The alliance meant that the CSU's independence would prevent the emergence of a truly separatist Bavarian political movement. This pragmatic arrangement has proven quite enduring in German politics, even as political Catholicism waned and the CSU began to more closely mirror the CDU as a more non-sectarian center-right party, albeit one with vestiges of earlier politics.
Sources
Dorondo, D. R. Bavaria and German Federalism: Reich to Republic, 1918-33, 1945-49. London: Macmillan, 1992.
Glaessner, Gert-Joachim. German Democracy: From Post-World War II to the Present Day. Oxford: Berg, 2005.
Rogers, Daniel E. Politics After Hitler: The Western Allies and the German Party System. Basingstoke: Macmillan, 1996.