Complex sentence: It has sold over 6 million copies in the United States and 16 million copies worldwide, became Lauper's best-selling album to date and is one of the best-selling albums of the 1980s decade.
Split into simpler sentences: It has sold over 6 million copies in the United States and 16 million copies worldwide. This makes it Lauper's best-selling album to date and one of the best-selling albums of the 1980s decade.