In the musical wicked which I suppose is canon and happens at the same time, Glenda reveals to Madame Morrible that the wicked witch of the west will probably show herself if her sister (the wicked witch of the east) is in danger. So Morrible summons the tornado to threaten the sister which coincidentally brings along Dorothy. Glenda secretly was good friends with Elphaba (WWotW) so wouldn’t have intentionally gotten her sister killed. There was a lot of politics and propaganda and stuff, but Glenda wasn’t really a villain, just a vain person who found it easier to support an autocracy. Someone who has read the books could probably explains it all, sorry if I’ve ruined your headcanon!

Probably the most exciting part of the trailer is that it all but confirms multiplayer which was probably the biggest missing element of the first game.