Political economy analyzes the relationships between economics, culture, society, and government and how changes in one area affect the others. Originally focused on production, trade, and their connection to law and customs, it expanded to consider labor as the true source of value rather than land. Marx's base-superstructure theory holds that the economic base determines the superstructure of legal and political institutions and cultural ideas. Music, like all cultural products, is shaped by economic forces and has evolved from ritual music to today's commercial industry.