Marineford

Marineford (マリンフォード Marinfōdo) is the main headquarters of the Marines (海軍本部 Kaigun Honbu, Marine Headquarters). It is where Fleet Admiral Sengoku and the three Admirals reside, along with many Vice Admirals and lower officers when they aren't assigned to another base. City surrounding marine HQ is inhabited by families of marine soldiers. The Marine HQ is one of the three great powers, alongside the Shichibukai and the Yonkou.

It is situated near the Sabaody Archipelago, and lies directly next to Mariejois on the Red Line. The only safe way to reach here is through the Gates of Justice. In FUNimation subs it was called Navy Headquarters.

East Blue's Newest Pirate
Shortly after the defeat of East Blue's most powerful pirates in the hands of Monkey D. Luffy, the higher officers here granted him his first bounty of 30,000,000.

Vice Admiral John Giant then announced to every high-ranking officers that the Marines there must be prepared to serve justice with all their might, and that there is no room for cowardice or moral justice.

Overtime, Fleet Admiral Sengoku spent his time residing here, giving orders to lower ranking subordinates, and taking out his fury over Monkey D. Luffy's repeated actions on his grandfather, Vice Admiral Monkey D. Garp.

Preparation for War
Whitebeard Pirates' second division commander Portgas D. Ace's public execution is scheduled to take place here at 3:00 p.m. sharp. To prevent Whitebeard and his crew's attempt to save their comrade, all of the Marines, along with the Shichibukai, has been summoned here to prepare for war. This may be one of the world's most shaking events. Jinbei, however, caused an outbreak in the headquarters in his refusal to cooperate, and was transferred to Impel Down.

Marineford has been declared a target by Monkey D. Luffy in his attempt to rescue his brother, Portgas D. Ace from his impending execution. He and Buggy the Clown have caused a mass breakout within Impel Down and is currently on their way there, preparing for an imminent assault upon Marine Headquarters.

Prior to Ace's execution, the normal citizens of Marineford were evacuated from town, leaving only the Marines to prepare for battle. Sengoku announced Ace's origins of being the son of Pirate King, Gol D. Roger, in front of the entire Marine forces.

The War Begins
After Sengoku revealed everything to the world, Whitebeard and his entire crew arrived, along with 43 allied pirate crews from the New World. With Whitebeard setting off a massive earthquake that caused two giant tidal waves to crash at Marineford, the war begins.