Progress for liberals is always progress for individuals. The core concern of liberalism is the happiness and contentment of individual human beings. John Locke argued that states existed to underwrite the liberty of their citizens and thus enable them to live their lives and pursue their happiness without undue interference from other people. In contrast to realists, who see the states first and foremost as a concentrstion and instrument of power, a Machtstaat, liberals see the states as a constitutional entity, a Rechtsstaat, which establishes and enforces the rule of law that respects the rights of citizens to life,liberty, and property.