We all know the key theme of the series is freedom. Luffy’s definition of Pirate King is “the man with most freedom on the seas”. To understand what One Piece is, let’s go back in time to the void century.

The Void Century is a gap where many things happened, from Joy Boy leaving his treasure, to the Great Kingdom being destroyed by the 20 Kingdoms which later on formed an alliance known as the World Government.

What was this Great Kingdom?

It was the homeland of the Lunarians which is currently now known as Mariejois.

Why was it destroyed?

The 20 kingdoms feared their powers and technology. The Lunarians created a tool that can control and manipulate the weather/environment. This enabled them to always have an advantage in wars as they had the natural ability to thrive in any conditions.

What is this tool?

This tool was later on called a weapon and was named ‘Uranus’

Where is this tool now?

The tool is still in Mariejois and is the ‘great treasure’ that Doflamingo mentioned

What exactly happened after the Great Kingdom was destroyed?

After the Luniarians kingdom was destroyed by the 20 kingdoms. The 20 Kings (led by Imu) formed the World Government and moved in to the Lunarians’ homeland and renamed it ‘Mariejois’. The surving Lunarians were enslaved and were put to extremely laborious tasks given their highly durable bodies.

The 20 Kings now known as the celestial dragons utilised the powers of the devil fruits to ‘reconstruct the world’

What happened during this reconstruction?

During this reconstruction, the sea was split and the ‘Red Line’ was formed (using ishi ishi no mi, gura gura no mi and more…) by merging hundreds of small islands together. Mareijois was placed at the center of this.

Why did the WG/ Celestial Dragons reconstruct the world?

With the Celestial dragons now in position and power as the ‘new gods’ of the world, they wanted to instil a process of governance and control.

Ultimately, the purpose was to limit what people can do and to hold dominance over the world. They grew in power and subjugated smaller nations under their banner. This led to an abuse of power and control.

Now that we have an idea of what the Great Kingdom was, let’s look at Joy Boy.

So, who exactly is Joy Boy?

Joy Boy was an explorer/pirate, he hated rules or any forms of restriction. He ventured from one island to another and was known to liberate it from tyranny.

The WG saw him as their greatest enemy as he had the potential to undo everything they had accomplished. Joy Boy gained a huge following base, and his powers and influence were tremendous.

Joy Boy and his alliance

Many nations disliked the new gods (WG) and their tyranny. So they created an alliance. Strong nations like Wano and Fishman Island were key members of this alliance. The Nefetari family decided to join this alliance too as they saw the corruption that grew in the WG.

The alliance’s purpose was to destroy the newly formed WG and liberate nations which have been forced under its banner. To do this, they needed weapons: Pluton and Posiedon.

What are these weapons?

In an effort to destroy the Redline, a warship with mass-destruction capabilities was created, this warship was constructed on Water 7. It was an immensely huge warship and due to its size, it couldn’t sail on its own. To move this warship, Zunesha was required. Only the heir to the Kozuki Clan is/was able to command Zunesha. This ship was called ‘Pluton’.

However, Zunesha pulling ‘Pluton’ would be left vulnerable, this is where the role of Posiedon comes into play. Bestowed with the abilities to control the sea-kings, the mermaid princess was to use her powers to create a barrier of sea-kings which would prevent enemy ships to approach it.

What was the purpose of Noah and Poseidon’s other purpose?

Noah was constructed to evacuate civilian during this destruction. Like Pluton, Noah was unable to sail on its own and the powers of Poseidon was necessary to pull it.

A great war during the void century

A great war engulfed the seas between JoyBoy and his allies versus the power-hunger WG.

The WG turned the tides to thier favour using ‘Uranus’. The war was so immense that it resulted into the the formation of the ‘grandline’ and its unpredictable weather (effects of Uranus) and the ‘calm belt’.

What is the will of D?

Having lost the war, Joy Boy’s close companions all adopted the ‘D’ in their name towards the end of Joy Boy’s adventure. The ‘D’ had multiple meanings, first, it was short for ‘defeat’ symbolisng thier loss. Second, it was a smile or laugh on its side, and third, it was short for ‘dawn’ as this is something that occurs as the sun rises and it will rise again. This relates to the fact that Joy Boy had the mythical Sun God fruit: Hito Hito no mi, model Nika

Essentially, the will of D is the will of freedom, and his companions have inherited his will in an effort that one of their descendants will achieve that freedom.

What is One Piece?

One Piece is a plan to restore the world to how it was originally. A single large open sea with no borders, free for everyone to explore regardless of race. To do this, ancient weapons are required to destroy the red-line.

However, that is not all. During the construction of the Red-Line, large quantities of gold (forcibly taken from smaller nations) were buried/stored in it. This is so only the WG has access to it.

By destroying the red-line, an abundance of gold would be released, therefore, giving the smaller/poorer nations a chance to get access to it.

Why was Roger early?

As mentioned, One Piece is a plan to restore the world and in doing so, there are a large number of civilians which need to evacuated. This requires Posiedon aka Shirahoshi, who at the time was yet to be born.

Why did Roger Laugh?

The last phase of the plan and the main reason why Joy Boy wanted to do it is so he could have the “biggest swimming pool party ever” with all the races from all ends of the world invited. However, he can’t actually swim due to his devil fruit.

Theory by 50thsun (https://www.reddit.com/user/50thsun)