Simplify the following text for a Grade 6 native English-speaking person.
Original: VolapÃ 1\/4 k became less popular after 1887 when Esperanto was published .
Simplified: Another reason for the decline of VolapÃ 1\/4 k may have been the rise of Esperanto . In 1887 , the first Esperanto book ( Unua Libro ) was published .