So we all know the Mushroom War is a huge plotline in the series as a whole.

What we know

  • It revamped the earth, now known as Ooo.
  • Ice King, Marceline, and Hudson are the only known survivors.
  • It was nuclear warfare.
  • It ended when Marceline was a child, with civilization destroyed.
  • A portion of Ooo was destroyed, leaving a crater.

What we can assume

  • It happened in the late early to mid 1900's. This can be assumed due to the fact that Lumpy Space Princess sets the year as 2009. While this was introduced before the Business Time episode, it was still introduced, making it crucial as it is a series plot, most likely thought up during developement. This can also be assumed based on the technology remain's appearance styling large headsets and old fasioned TVs. There also appear to be relic trains and railroads, possibly reffering to the start of the railroad industry. More importantly in Finn the Human's trailer, the airships fasion those of World War I.
  • Marceline was human during this war.
  • The majority of the land was sunk below the sea. This is shown through Ooo being a continent as well as the underwater ruins with the two dead people.
  • The Lich plays a significant role. In Finn the Human, the cease of his existance, creates the Farmworld universe, where this war never appeared. This can be proven because Finn is a regular boy and Jake has no magic powers, as well as Finns parents being alive. He can also be presumed to be one of the contestants of this devistating war as mushroom clouds appear behind him. Alternatively, the Lich could be a Weapon gone rogue. The Lich is a being of pure evil, possibly vreated by humans as a weapon aginst the their rival, however being made of pure evil, he went rogue and attempted to destroy humanity, to which he succeded. However when he attempted to kill again, he was defeated by Billy.
  • The nuclear cloud created the Hyooman tribe. They are a mutated race who appear to have survived, but in turn changed in appearence, and choosing to live underground instead of the rubble.
  • The nuclear warfare created the creater. Being a World War, as shown in Issue 4, we can allude that multiple quantities of bombs were dropped. The impact resulted in the lands destruction. This combined with the Meteor Simon discovered, must have destroyed the land. We can also assume this because, as shown in Sons of Mars, several human foods were sent into space.
  • Simon knew of the war before it began, and he knew the aftermath. In Holly Jolly Time, he said the crown showed him terrible visions.
  • Humans for the most part ceased to exist. Finn is the only known human, while Susan is pressumed to be a Human due to Finns reaction when touching her below her headgear. Aside from this the Reinicorns state that they believed humans were extint. Even then, the mutated creatures that arose from the aftermath found a great taste for human, again shown through the Reinicorns. So even if some Humans survived, through time, they were dying out, eaten by other creatures, explaining why Finn was abandoned.
  • Ice Kings desire for princesses comes from here. His love left him, and as his mind decayed, the war progressed. In the end, most humans were killed, and Simon knew this, also knowing he would never see his princess again. He cried when looking through the scrapbook, and he mentally snapped, with this the Ice King was born, as such his main desire was princesses, as his old self wanted to be his with one true princess.
  • The radiation resulted in the primitive Candy Kingdom. This would make sense as the radiation had already mutated humans and signs, so why not candy on the ground? The mutation of course occured through time as the remains of radioative weapons leaked into the ground and eventually onto the objects on the ground such as Candy.
  • After Simon lost himself, the Ice King went to a tundra area where he created the Ice Kingdom. This can be assumed because of Gunter. Penguins in our time are known to live in the cold areas, as such in a post apocalyptic time, those who survived would live in the tundra remains.
  • Marceline and Hudson were transformed into vampires. She was a human during the war, however by the end, a vampire.
  • Ooo is the remains of land in Asia. The Reinicorns know Korean, as well as Bubblegum knowing Japanese. Lady also spoker of Vietnamese noodles. This would make the Ice Kingdom Siberia.