Marineford and the Post War arcs are the twenty-second and twenty-third story arcs in the One Piece story.
You can find reviews of the previous arcs here:
Battle of the Decade
Marineford is the cumulation of the last few arcs in One Piece. Some of the strongest pirates we know of, Luffy and his allies, and the marines are all heading towards Marineford, and we know they are going to clash and cause a cataclysmic event that will change the world.
We don’t have a great understanding of the Marine’s strengths, or that of the Whitebeard Pirates, but they have been hyped up enough in the past few arcs that we know there will be a lot of death on both sides when they clash.
Dozens of chapters go by, and we get to discover the strengths of so many characters in the world. Oda does an amazing storyteller and world builder.
The amount of behind the scenes storytelling that is going on is truly is great to know.
When a clash of titans like Marineford happens, all you can expect is events that make your jaw drop.
Marineford is the starting point for the second half of the story. So many things that happen in Marineford have huge impacts in the arcs coming afterwards, and probably ones to come.
Even when you think nothing else can shock you, you’ll be surprised by how wrong you are.
Some of the events will leave you shocked, some will leave you speechless, but they all will make this arc one of the best arcs in the story.
They don’t have a lot to do with the StrawHats, so you don’t have as deep of a connection to the characters, but despite that, Oda knows how to connect readers to the characters in the short amount of time you know them.
Post War is a bit of a small arc. It doesn’t have a lot to do with Marineford itself, but it is a nice resolution that lets us cope with the events that just took place and set up the next saga of One Piece.
It’s also a nice Segway into a two-year time skip that takes place inside One Piece.