I predict there will be 4 major battles before Luffy becomes the pirate king.
The first is going to be the Revolutionary Army vs the World Government. This battle is going to take place at The Holy Land. The RA will launch a surprise attack thereby kidnapping Celestial Dragons to rid the world of them. After 3 weeks of this, the WG will have found out where they are hiding and that they are responsible so they will march their full forces but, the RA will ambush them. The casualties on the WG side will include Greenbull and all the vice admirals except Garp and Momomga. Plus they would have lost about 60% of their troops. On the RA side Belo Betty, Koala, and Lindbergh would be captured and sent to Impel down.
The second major battle will be the RA + the Red-Haired Pirates + the Heart Pirates vs the WG at Impel Down. they will have Morley dig down to level 6 but the WG will be waiting for them. This time, they will have the God's Knights, the Gorosei, and the rest of their forces with them. Fujitora's and Sabo's DF awaken during this fight. When Fujitora's DF awakens he finds out that he can fully control gravity. He can make it so that there is no gravity, a little bit of gravity, normal gravity, and so much gravity. When Sabo's DF awakens, he can control any fire source, extinguishing and fueling it anytime he needs, plus he can make his flames white. Key moments include Fujitora switching sides mid-battle, Sabo defeating Akainu, the god's knights getting bodied by Shanks, and Benn Beckman getting killed by Garling. the WG will be completely defeated with Imu, Sengoku, and Koby barely making it out alive.
