(Magna Mundi Gold 1.5)
Playing as Brandenburg because I heard it's a good choice for uniting Germany. I started with making Saxony my vassal diplomatically, then annexed it. Moved on to Mecklenburg and annexed it thorugh war and then made their ally Pommern my vassal which I later annexed. After that I annexed Lübeck through war. By this time I had already realised that the Ottoman Empire was gonna be a problem for me so instead I went east to take Danzig because of the trade center and also Warmia while I was at it. Along the way I lost the provinces Neumark, Dresden and Erfurt to the Ottoman Empire. Right now I've got a +200 relation with both Russia and the Ottoman Empire so hopefully they'll leave me alone while I try to expand further west (started with Hamburg already). A little worried since they've both got cores on some of my provinces.
From here it is probably impossible to unite Germany. Firstly I would have to fight tens of thousands of troops and then I would have to take many of their provinces to get one because they are so big.
What did I do wrong? Bad luck? Not playing fast enough?