Hand Island is a non-canon island in the New World, famous for its craftsmen, that was formerly under the protection of Whitebeard. After Whitebeard's death, the island was ruled by the Marine Commodore Bilić, until he was defeated by the Straw Hat Pirates.
After the Whitebeard Pirates' flag lost its protection value, some pirates began to attack the island and the MarineCommodoreBilić intervened, protecting the island in exchange of inhabitants' submission and male adults' enrollment in the Marines, starting the construction of the base and of the Josephine cannon. At the same time Diego's son, Regis joined the Marines. A year later the cannon was completed and Bilić started to shoot everyday at the island.
Later Regis was imprisoned for rebellion against his superior Bilić.
Episode of Luffy
Due to escaping from a Marine fleet, Franky used the Coup de Burst to make the Thousand Sunny fly away and fall on Hand Island, which destroyed Diego's house. Meanwhile, Koby and Helmeppo arrived on the island in order to investigate Bilić.
After Luffy saved Regis, Bilić learned about the pirate's presence on the island, he threatened the inhabitants that he would destroy their city if they didn't reveal where Luffy was.
In the end, Luffy fought and defeated Bilić and destroyed his base. Koby and Helmeppo then brought him to court-martial for his actions, which freed the island from his tyranny.