Tell the Catholic Church that, for they were actively preaching against Polish independence from the pulpit in the 19th century.
Of course. Official politics of Vatican is to support bigger Catholic power, wealthiest Catholic magnate, etc.
Now, you also have that general trait of all European non-Slavs who would all tell you how Slavs are inferior. And that necessity to degrade Slavs (ie Sarmats) exist from Greek and Roman times and via early middle ages during era of slavery and as it was later defined as `Drang Nach Osten`. Meaning, every push against Slavs is justified. Grab what you can from Slavs, people, land, whatever. You can say how are Slavs outlawed by Christian Churches. Sure, its publicly untold but, whenever Church (Catholic, Orthodox or Protestant) leaders can they will support non-Slavs against Slavs. On example of Poland, you have that additional problem that all Catholics are better Catholics then Poles and more desirable to rule Europe.
So, to put it in modern context. If for example France occupy Poland, you think Poland will resist? I think resistance would be very weak. Catholic Church would subdue Poles and make them content to new rulers.