Complex sentence: At the end of 1999, Warner Bros. Movie World started a cooperation with Six Flags Inc. As part of this cooperation, Warner Bros. gave the license rights to Six Flags, who in turn managed the park under the name Warner Bros. Movie World as a licencee.
Split into simpler sentences: At the end of 1999 Warner Bros. Movie World started a co-operation with Six Flags Inc. Warner Bros. gave the license rights to Six Flags. In response Six Flags had managed the park under the name Warner Bros. Movie World as a licencee.