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IOTL Bavaria came close to inherit the whole of Baden. In 1817 when Grand-Duke Karl lost his only son, the only agnate member of the royal family was his childless uncle Ludwig. With the semi-salic law in place that meant that after his uncle, the next in line would be his sister, none other than the Queen of Bavaria.
This was avoided by "relegitimizing" an agnatic morganatic branch of the family.

WI Bavaria does get Baden in - say - 1830 (Ludwig's OTL death). What does this change?

Baden connects mainland Bavaria to its Palatinate so hurray for territorial contiguity! Württemberg and the Hohenzollern principalities are now surrounded by Bavaria, except for a thin lake shore in SE Württemberg that oversees Switzerland.

Does Bavaria-Baden have more of a say in the Germany Confederation to threaten Austro-Prussian dualism?

Bavaria-Baden in German Confederation.png
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