Poland expanding to the West in Middle Ages - possibilities

Originally posted by kasumigenx
I think Boleslaw the Brave could annex the Polabian lands.

Well, he did conquer Lusatia, so theoretically he could get also other Polabians. Problem is he did it fighting against HRE, so even if he's successful sooner or later (quite quickly IOTL) the Empire WILL strike back. Poland simply was too weak to fight all HRE for any longer time with hostile Kievan Ruthenia behind its back. Boleslaus was an excellent warrior, but he antagonized most of Polish neighbours (HRE, Bohemia, Kiev), so his son was in real trouble. However....
In 1028 Mieszko II marched with his army against emperor Konrad II. His goal was to help Ernest II of Swabia, a pretender to imperial throne. But Mieszko was too late. Ernest was already defeated and captured. Polish army devastated part of Saxony, probably also lands of Veleti. Later, allied with Hungary, Mieszko II caused a lot of trouble to Konrad II, but eventually Hungarians made a separate peace and Mieszko was defeated by a coalition of HRE, Bohemia and Kiev.
But WI if Mieszko II attacked a year earlier and helped Ernest defeat Conrad? As reward he keeps Lusatia and carte blanche in Veleti lands. Together with Humgarians he neutralizes Bohemians and should be strong enough to deal with Yaroslav the Wise of Kiev.
Should he succeed (with some luck), Mieszko might become real power. However, Bohemia was part of HRE and Ernest might have some problems with explaining his followers why he gives away lands of the Empire.
I might have a solution. Let's make Mieszko's Poland part of the Empire. Poland becomes kingdom (yes, kingdom) in the HRE. After all IOTL in 1085 Vratislav II of Bohemia received a title of king of Bohemia (and Poland) from emperor Henry IV. Why coud not Mieszko get the same 50 years earlier?
I wonder if Mieszko II would go for it. On one hand, Poland would have had to obbey the emperor, at least formally. OTOH, Polish king would become one of the most powerful lords of the HRE, second only to king of Germany. Some Polish lords might be unhappy with that, but victorious Mieszko II might be strong enough to push it through, after he deals with internal problems (and there will be a lot of them).
 
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