What major events in the Forgotten Realms marked transitions from one edition of D&D to another?
- Anybody can ask a question
- Anybody can answer
- The best answers are voted up and rise to the top
You've found them all.
The Forgotten Realms was first published for AD&D 1st edition. When 2nd edition came out, the change in spells and available classes was explained through the Godswar aka The Time of Troubles.
The introduction of D&D 3e was exceptional in that there was no overarching, global event introduced to explain the rules changes. Karsus's Folly was introduced with 3e as a historical detail that further developed the history of Netheril and explained some changes local to the Anauroch and some new game elements, but it wasn't the same kind of global upheaval—it was more of a retcon slipped in as undisruptively as possible.
The Spellplague (and hundreds of years) explained the shift from D&D 3.x to 4e, and the Sundering did the same for the transition to 5e.