There are several reasons why I think the Straw Hat Grand Fleet will turn up at Wano, attack the World Government and, by doing this, start the Great War.
There are a few things we know about the Straw Hat Grand Fleet:
– They are numerous, over 5000 strong. So they would actually be capable of attacking a fleet.
– They will cause some kind of event that will rock the world.
– They have a Vivre Card of Luffy.
This last point is important because I think that this is the reason why they would be showing up at all: because they saw Luffy’s Vivre Card burning up rapidly. There are in my opinion two moments where this could have been severe enough to send them in a panic and let them decide to head to Wano:
- 1-When Luffy almost got ‘killed’ by Kaido before his Awakening (or even before, when he got thrown off of Onigashima. I don’t think this will be the reason though, because while the Raid is taking over a year in real time, only 1 day has passed in One Piece universe: too little to arrive in Wano on time to intercept the World Government’s fleet. Of course, this depends on how quick the World Government is planning on moving into Wano after the defeat of Kaido (which I am assuming is immediately).
- 2-When Luffy was fighting in Udon and got infected with one of Queen’s bioweapons by the head jailer. This could have been enough to let his Vivre Card burn up rapidly and also give enough time for the Straw Hat Grand Fleet to head over to Wano to check ‘What’s up?’.
Of course, the Straw Hat Grand Fleet would be heavily assisted by Zunisha who is conveniently placed behind the World Government’s fleet and is probably very able to take it out all by itself.
I think the Straw Hat Grand Fleet taking out a World Government’s fleet would create the perception at the World Government that Luffy knows more than he actually does (about the Void Century) or is planning on being their direct adversary (while we as readers know the Straw Hat Grand Fleet would just have been acting on their own accords).
Together with his recent Devil Fruit Awakening, this could be a good enough reason for the World Government to declare war on Luffy who does not even realize and will probably sail to the next island without even realizing he is the center of a new war.