Otherwise, this quest will never have enough settlements to finish. Once the player character fast travels there, they may meet Preston, Ronnie or an unnamed Minuteman there, to initiate Defend the Castle. This is likely due to Preston being at The Castle after Form Ranks is skipped. Upon completing radiant quests for the Minutemen, they may be automatically completed without talking to Preston Garvey, once the objective has been completed. In this case Defend the Castle starts instead. The Minutemen are now strong enough that we can think about taking on the Institute. Quest Complete - Trigger Defend the Castle
I should work on building up support across the Commonwealth. The Minutemen are not strong enough yet to take on the Institute.
I should talk to Preston Garvey about how the Minutemen can help me destroy the Institute. Talk to Preston Garvey about the Institute.