the Clone Wars, at the begining the Republic was democratic and the jedi were powerfull. After the wars the Republic became the Empire and was ruled by an evil emperor, the jedi were almost extinct and the Sith were in control. Everything was changed and in the OT they are still struggling against the same empire. So the clonewars was very important I think.
Vader Offering Luke To "Rule The Galaxy as Father And Son" this led the emperor to beleive vader would want to take over (heir to the empire conversation between luke and jade) thus leading to the confrontation with the emperor trying to convert luke leading to his demise leading to the fall of the empire leading to mara jade unemployed and thrawn coming to power leading tohim finding master cboath leading him to hunt down luke and leia and the twins leading to luke falling to the darkside.