Poland was ruled by Soviet - backed government after the Second World War . Solidarity movement was a key factor in the collapse of communist regime . Centrally - planned economic system replaced by free market economy . Poland joined the European Union in 2004 .
Poland was ruled by Soviet-backed regime after the Second World War . Solidarity movement became a key factor in the fall of communist regime . Centrally-planned economic system replaced by free market economy . Poland joined the European Union in 2004 .