Dream SMP explained

(12) Doomsday

This era was based around the destruction of L'manburg, and the remaining citizens' attempt to save the dying nation.

Dream arrived an hour early and announced his plan. To attack half an hour early and catch the L'manburgian's off-guard, ensuring victory. Techno was reluctant, because he didn't feel prepared to fight half an hour early, he had planned on using the time to brew potions, but was able to cut potion production short as he found the remainder of the potions from the attack against Schlatt, where most potions went unused.

Dream, Techno and Phil devised a plan. To have Techno fight  alongside the hound army, buying time for dream, making him able to set up the "superweapon" in the skies above L'manburg. When Techno gave them the signal, *shooting a firework*, Phil was to summon Techno's withers and begin the destruction. 

Techno arrived at L'manburg 20 minutes before planned, tommy becomes shocked when he checks. Tommy called for Tubbo and the others to come to L'manburg, and the army are forced to assemble, unprepared because fundy sabotaged the supplies.

The L'manburgians were able to fight off the majority of the hound army, but the fight turns south when techno shoots a firework into the air, sending a signal to Phil, who then summons multiple withers. The destruction of L'manburg begins.

Tommy attempted to give Techno a "The reason you suck" speech to techno, saying he betrayed him, but he was quickly cut off by techno, and he turns it back on tommy. He said that tommy had no right to say techno betrayed him, when he was the one that used up his supplies before leaving him to join the corrupt government that had been persecuting both of them. Techno then went on to call out the other L'manburgians for trying to execute him when he was just trying to live in peace, then saying that they were the first ones to attack, and the brought the destruction of L'manburg upon themselves.

Phil continued to summon withers, but they weren't doing much damage. Dream then revealed his "superweapon", an obsidian grid lined with TNT canons. This ultimately destroyed what was left of L'manburg.

Despite not actually being a citizen, jack manifold decided to fight alongside L'manburg as he believed his home, "manifold land" was too close to the nation for comfort. Jack lost his last canon life in a fight with techno, but he was revived after a trip to hell, and returned with all 3 canon lives intact. All of jack's belongings were burnt in the war, and he realized he never actually needed to fight in the war, as he wasn't a part of L'manburg in the first place. Manifold land remained unharmed, neither dream nor techno actively want to destroy it. Jack promptly swore revenge on techno.

Though it was clear the L'manburgians were going to lose the war, they continued to fight. The L'mantree, the last remnant from wilbur's presidency is destroyed. Surprisingly, not by TNT or withers, but by Niki burning it down.This meant that nothing remained of the L'manburg they fought for in the war of independence, and they ended up giving up hope and surrendering the war, letting the TNT and withers turn their fallen nation into a chunk error. As it is being destroyed, tommy, tubbo, quackity and ghostbur sing "my l'manburg" one last time.

The superweapon is disabled, and Tommy confronts Dream atop the obsidian grid. Dream decides that messing with Tommy is just too fun for him to kill Tommy off, and declares to Tommy that their war will never end.

Dream names Punz as interim leader of the Greater Dream SMP, presumably to reward him for his efforts as a mole within L'Manburg. Techno, Phil, and Dream meet up one last time. Dream declares the Doomsday War as an unequivocal victory before . Meanwhile, the two Anarchists retrieve the survivors of the Hound Army before accepting a homeless Ranboo into their ranks.