Complex sentence: The group released album named "The beauty" in 1974, which sold more than 1 million copies and its title "The beauty" is called 30,000,000 citizen's song (in 1974, South korea's population was almost 30 million).
Split into simpler sentences: The group released album named "The Beauty" in 1974, which sold more than 1 million copies. Its title song "The Beauty" was called "30,000,000 citizens song" (in 1974, South Korea's population was almost 30 million).