I do remember reading about that, but while they did develop an advanced representational gov't, I thought it was never fully in place. like the nobility and others, and the church were constantly meddling in it to make sure they kept their traditional power.
Regardless, In the 1600's Poland fought a bunch of bad wars, and got clobbered. In Poland it was called "The Deluge"... everything went to shit at once. Ukraine revolted, and they fought Russia, Sweden, and various German princes all at the same time. Bad idea. This, coupled was coupled with the growth of Prussia to the west as a great power, and Russian growth as well to the East. in the 1700's Prussia, Austria, and Russian simply divvied Poland up. the country was so devastated it had no army to resist.
Poland had somewhat of a revival under Napoleon, although never formally independent. It didn't become an independent nation again until 1918.
then of course at the start of WWII, Poland was in the worst possible geographic location, anywhere on the planet.
Polish government wasn't exactly representative.
The Polish King was elected to serve the Nobility. The Sejm (Polish parliament) was only for nobility. Serfs basically had no freedom.
Polish decline occurred largely because country was broke after fighting too many unsuccessful wars. Hell, even Sobieski foresaw the decline of the empire.
The second half of the 18th century Polish politics were a mess and constantly fiddled by outsiders as the country was broke. Nothing could get done in the Sejm either. It was a joke, reminds me a lot of US congress at the moment. An empire clearly on the decline, and unable to do anything politically.
Tadeusz Kosciuszko was promising freedom to the Serfs who fought in the 1794 rebellion against the Russians. His scyth militias even had a few victories over Russian regulars.
Naturally, the Catholic Church was against losing the Serfs (ie. loss of money, and power) and thus did their best to sabotage Kosciuszko and aid the Russian.
At outbreak of world war II Poland was surrounded by enemies on 85% of its borders. It was a miracle Poland lasted as long as it did.
As for Napoleon, the Dutchy of Warsaw was nothing. Following end of Napoleonic wars the Kongress Kingdom under Russia was also a joke. There was some freedoms early, but within a few years they were slowly removed by the Russian crown. Only great thing that happened was the 1830 rebellion where Polish troops refused to march on the Belgians and fought the Russians instead. IIRC was also one of the first times Finnish troops saw battle for the Russian empire.
God's Playground is probably the best source for Polish history.
I still loved the Soviet reviews of it. Along the lines of, it is great until the author reaches the 20th century.
Otherwise, the Polish Way by Zamoyski is decent as well.
As for Kosciuszko the best biography I read was The Peasant Prince.
I do recall Detroit has a statue of Kosciuszko couple blocks from that weird star intersection downtown.