Simplify the following text for a Grade 10 native English-speaking person.
Original: The Albigensian Crusade or Cathar Crusade ( 1209 â `` 1229 ) was a 20-year military campaign initiated by the Catholic Church to eliminate the Cathar heresy in Languedoc .
Simplified: The Albigensian Crusade or Cathar Crusade ( 1209 â `` 1229 ) was a 20-year military campaign . It was initiated by the Roman Catholic Church to eliminate the Cathar heresy in Languedoc .