The problem with the Polish-Lithuanian Commonwealth was that simply put it was less a unified country and more a group of self-interested nobles who happened to speak the same language. While in theory the PLC controlled a large amount of (relatively) rich territory, in practice this territory can be divided into four portions: Polish "core territories," (i.e. Warsaw, Krakow, Greater Poland, Lesser Poland, etc.), Lithuanian territories, Ukraine, and Russian territories.

Most of Poland's economic and military strength came in the form of its rich agricultural lands in Poland and on the back of its heavy noble cavalry. This strength was dissipated by being controlled by hundreds of Szlacha nobility who could essentially tell the central government to piss off if they didn't like it. As such Polish military campaigns were typically conducted with relatively small numbers of troops, for instance, the Polish-Russian War of the 1610s had around 12,000 Polish troops against a much larger Russian force of some 30-40,000 troops. However the Polish cavalry arm was superior to its local opponents of the time and despite numerical inferiority were nonetheless able to thrash much larger opponents-in 1605, a 10,000 man Swedish force under Charles IX outnumbered its Polish opponents by 3 to 1, and ended up suffering in excess of 70% casualties in a devastating rout. However it should be noted that the Polish force consisted primarily of the general's personal forces, what forces he could afford to pay for, and his friends' and allies troops, as the Polish crown refused to pay for any defense force. And this was the sort of silliness that weakened Poland.

In the 1650s, two events happened that permanently destabilized Poland. First, a group of Cossacks rebelled in Poland's Ukrainian territories, eventually seizing control in a brutal civil war and pledging loyalty to the Russian crown, thus depriving Poland of its extremely fertile farmlands along the "Black Earth" belt as well as forcing it to waste valuable troops and funds attempting to combat the uprising. The aforementioned Polish cavalry were also much harder to replace than other troops due to their high cost and rigorous training regime, weakening the Polish military. Then, Swedish troops invading Poland conducted what essentially was a scorched earth campaign in Poland's core areas, during a period known as the "Deluge." While the Swedish troops were eventually expelled from Poland, they left a devastated Poland behind, further weakening the PLC. The sudden loss and devastation of so many territories, combined with the rise of Russia, essentially reversed the power equilibrium between Russia and the PLC.

The PLC also had a nasty clause in their parliament called liberum veto. Liberum veto allowed any noble in the parliament to completely shut down any legislation. While in theory its purpose was to head off a dominant monarch, in practice foreign-influenced nobles were pressured to enact the veto in response to any attempt by the government to reform or act against the wishes of the foreign power, be they Russia, Prussia, or Austria.

The ensuing paralysis of the government, combined with a fall in Polish economic and military strength, left it in no position to resist the other European powers when they moved troops into Poland in the First of the Three Partitions.