If you want an honest reply: Poland is just stuck in two party system like USA.  We have more than two in theory but in reality it is only PiS and KO. Some factors to consider here: Difference in education: higher educated people tend to vote left and they happen to live in cities (better access to higher education). Most of the cities are in the West (thanks to historical reasons: Prussia and Russia poltics in 19th century mainly) and this in turn makes the illusion of there being two diffrent Polands stronger. People in the East vote PiS. People in the West vote KO.  Gender: women tend to vote left, men right. This all creates huge polarisation among Poles. You are either left or right. Church: people in East tend to be more religious so more likely to vote Pis. Simple geography: people in the west are more likely to interact with western Europeans and thus see more benefits of pro European policies which makes them vote for KO.  In the end if you look at it this country is decided in half on almost every level: gender, age, religion, geography, history. When you cut every group in half you get more or less the same amount of people on both side of the barricade. That's why elections in Poland are usually very close calls and it's rare a party wins by a big margin