in OTL, one of the ways Germany could have unified but didn't was to annex Austria, albeit it did win a war easily against them. There even was a term for it, Grossdeutsch, which contrasts to the Kaiser's founding of Germany in 1871 which is a Kleindeutsch. Bavaria, which is similar to Austria culturally and linguistically, was annexed despite its Catholic majority and remember, the Second Reich was quite anti-Catholic even for its time. What is a POD no later than Napoleon's defeat at Waterloo that can be used to get a Grossdeutsch???