You can't list the major events, they're all equal contributories.
Discovery of the Force, Hyperspace, the foundation of the Republic and Jedi, the first Jedi outcasts which would put the Galaxy into some 20 000 years of turmoil, the rise and fall of the Empire, the Yuuzhan Vong invasion.
__________________ Recently Produced and Distributed Young but High-Ranking Political Figure of Royal Ancestry within the Modern American Town Affectionately Referred To as Bel-Air.
And you have to understand that history of any sort is a compounding continuum, it's not fragmented "events" that occur with no rippling effect. If you measure by most influential on galactic affairs, then obviously the earlier events.
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.
__________________ If star wars takes place in a Galaxy far far away, why does OB1 have a British Accent?