The map above depicts the various ways Europe has been divided.
Historically, the great divide between Eastern and Western Europe has been the Catholic/Orthodox line (Gold Line). Those to the west of the line kept religious allegiance to Rome and generally politically-separate from the Constantinople-based Roman (Byzantine) Empire. People east of line stayed loyal to the combined religious and temporal leadership in Constantiople by being Eastern Orthodox.
The red line is many Cold War-babies dividing line between the two Europes. The Iron Curtain shaped many people's perceptions of a free, liberal west and a Communist, dictatorship east. The west began forming a common European community while the east were satellites of Moscow.
The late twentieth and early twenty-first century is one of Western European ideals, and maybe therefore Western Europe itself, expanding into the east. The light green countries are members of the European Union which itself is the descendant of the European community started by the Western European states during the Cold War. Pink countries are official candidate states up for a vote to be allowed into the European Union while peach countries are states with either significant government or popular support to join the union.
While new European Union members and those countries that wish to join the union have distinct cultural traits that set them apart from traditionally-thought Western European countries, western ideals are beginning have taken hold in these countries because of the desire to join the union. Open markets, liberal election laws, and better minority rights and recognition are just some things thought impossible in "Eastern Europe" just twenty-five years ago. Even countries not thought of as European at all, like Turkey and Georgia, have begun adopting Western European thoughts and policies to join the union.