Complex sentence: When the Tamers entered the Digital World, WarGrowlmon again appeared to fight Beelzemon but because of Takato's rage and his desire to kill Beelzemon (who had killed Leomon), WarGrowlmon digivolved to Megidramon.
Split into simpler sentences: When the Tamers entered the Digital World, WarGrowlmon again appeared to fight Beelzemon. However, because of Takato's rage and his desire to kill Beelzemon (who had killed Leomon), WarGrowlmon digivolved to Megidramon.