A utopia is a place, state, or condition that is an imagined ideal world with respect to laws, politics, and social conditions. A dystopia is the opposite of a utopia. It is an imagined nightmare world, often set in the future. The characteristics of utopias include peaceful governance, equality for citizens, and a safe environment. In contrast, the characteristics of dystopias include a controlling and oppressive government, extreme poverty, and the banning of independent thought. Utopian and dystopian fiction are genres with roots that go far back in literary history. Authors have used both to entertain their readers and to criticize their contemporary culture—using utopias to create appealing scenarios and dystopias to create alarming ones. During the twentieth century, these genres have at times blended together with closely related genres such as science fiction and climate fiction, and many of the works have become literary classics.