GRRM originally intended to end ADWD with two major battles before pushing them to TWOW:

There were a lot of cliffhangers at the end of A Dance with Dragons. Those will be resolved very early. I’m going to open with the two big battles that I was building up to, the battle in the ice and the battle at Meereen—the battle of Slaver’s Bay. And then take it from there.

In this post I am going to discuss the two four major battles (Ice/Fire/Blood/Steel) that should take place in the early stages of TWOW and have readers on the edge of their seats from the start.

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Background

GRRM has planned to open TWOW with "a smash"

I think we’re gonna start out with a big smash with the two enormous battles

and I think its probable that GRRM still wants to maintain the intercutting (at least between Ice/Fire)

My original intent was to end DANCE with the two big battles, yes… intercutting between the two of them, each told through several different points of view.

but at least around the same time we should get views of the somewhat "smaller" battles, the Battle of Blood (Oldtown) and the Battle of Steel (Storm's End).

Let's take a look.

Battle of Ice

Location: Crofter's Village (~3 days ride from Winterfell)

POV(s): Theon/Asha

Factions: Stannis vs. the separate Manderly/Frey/Bolton forces

Magic: Weirwood on the lake (Bran/Bloodraven), "Lightbringer"

Confirmed Events:

• From the "Asha Fragment" we know that Crowfood Umber was defeated and killed by the Freys
• From TWOW, Theon I we know that Stannis is aware of the Karstark's treachery, that he has some sort of plan and that he has been recommended to "give Theon to the tree".
• From GRRM we know that Stannis is going to sacrifice his daughter Shireen. With that in mind, it is assumed that Stannis wins the Battle of Ice.
• In January, 2016, GRRM was revising a Theon chapter
• GRRM has at least two Asha chapters complete (which he mistakenly thought he had read to readers before)
• In June, 2020 GRRM confirmed he was working on an Asha chapter (unknown when exactly they take place)

Of late I have been visiting with Cersei, Asha, Tyrion, Ser Barristan, and Areo Hotah

If interested: The Nightlamp Theory by u/cantuse

Battle of Fire

Location: Meereen/Slaver's Bay

POV(s): Victarion/Barristan/Tyrion

Factions: Ironborn/Queen's Men/King's Men/sellswords/Slaver's Alliance

Magic: Moqorro, Dragonhorn, Dusky Woman, Viserion, Rhaegal

Confirmed Events:

• TWOW, Barristan I takes place inside Meereen just prior to the battle
• TWOW, Barristan II shows the beginning of the battle as they ride out and begin to form up, the Slaver Alliances miss a chance to flank them, the ironborn arrive and begin fighting the slaver ships
• TWOW, Tyrion I shows Tyrion (+Penny) join the Second Sons
• TWOW, Tyrion II shows Tyrion with the Second Sons after the battle begins, the Second Sons switch sides again, the Slaver Alliance seem to be losing as Rhaegal is flying in wide arcs over the city/bay
• TWOW, Victarion I shows the Ironborn just before the battle, Victarion has 3 men ready to blow the dragonhorn
• In June, 2020 GRRM confirmed he was working on Barristan/Tyrion chapters (unknown when exactly they take place)

Of late I have been visiting with Cersei, Asha, Tyrion, Ser Barristan, and Areo Hotah

• In August, 2020, GRRM confirmed he was working on a Vic/Tyrion chapter (unknown when exactly these chapters would take place):

For the nonce, it is what it is.   My life is at home, on hold, and I am spending the days in Westeros with my pals Mel and Sam and Vic and  Ty.

Battle of Blood

Location: Oldtown/Battle Isle/Hightower

POV(s): Sam/Aeron

Factions: Euron Greyjoy, Redwyne Fleet + Hightower defenses

Magic: Ravens (white/black ravens hate each other), Glass Candles, "Missing" Hightowers (Leyton/the Mad Maid), Euron + Blood Sacrifice/Summoning + Valyrian Steel Armor, Faceless Men (Death of Dragons, Dragon egg, etc)

Confirmed Events:

• From TWOW, Arianne I we know that krakens have been spotted:

"And krakens off the Broken Arm, pulling under crippled galleys," said Valena. "The blood draws them to the surface, our maester claims. There are bodies in the water. -TWOW, Arianne I

• From the Forsaken, we find out that Euron is headed toward Oldtown with priests lashed to the prows of his ships and there are numerous potential visions that potentially speak to the upcoming battle

I saw towers by the sea, submerged beneath a black and bloody tide. That is where the heaviest blow will fall."

and:

"Only their shadows," Moqorro said. "One most of all. A tall and twisted thing with one black eye and ten long arms, sailing on a sea of blood." -ADWD, Tyrion VIII

If interested: The Eldritch Apocalypse and What Exactly is Euron Summoning?

• In addition to the Forsaken, there should be at least one more Damphair chapter

With the use of the word "the", are you implying that there will only be one Damphair chapter in WINDS?

GRRM: No. -SSM, Baltimore and DC: 12 June 2016

• In August, 2020, GRRM confirmed he was working on a Sam chapter (unknown if this would take place before/after/during the battle):

For the nonce, it is what it is.   My life is at home, on hold, and I am spending the days in Westeros with my pals Mel and Sam and Vic and  Ty.

Battle of Steel

As speculated by many, two large battles will take place early on, a 'battle of ice' (presumably at Winterfell) and a 'battle of fire' (presumably at Meereen). A third battle has been added, namely the assault on Storm's End by Jon Connington's forces. Originally this was going to happen off-page, but GRRM decided it really should be shown. Possibly because we've seen Storm's End under siege forever and it might be cool to finally see the place under full-scale assault. -SSM, Worldcon: August 2011

Location: Storm's End (which has never been taken by force)

POV(s): Jon Connington/Arianne (post battle)

Factions: fAegon and the Golden Company, Mathis Rowan and a token force, Gilbert Farring and 200 men

Magic: magic in Storm's End's walls

Confirmed Events:

• In TWOW, Arianne II, we find out that Haldon Halfmaester claims they have taken Storm's End but Mace Tyrell is bringing an army from King's Landing
• Mace Tyrell had previously left Mathis Rowan in charge of a token force to siege Storm's End, while he took his army to King's Landing for Margaery's trial
• fAegon planned to lead the assault:

"He did, actually," the prince said, "but I won't. Harry's an old maid, isn't he? You have the right of it, my lord. I want the attack to go ahead … with one change. I mean to lead it." -ADWD, The Griffin Reborn

• Since TWOW, Arianne II ends with Arianne choosing to sail to Storm's End (unless the GC is lying and planning to use her as a hostage, doubtful imo)
• GRRM originally planned a "complementary chapter" to the Arianne chapters which would presumably be a Jon Con chapter

so I wrote the two Arianne chapters and was going to write a third... and a chapter from another POV that would be a necessary complement to them, and...

• Dany has a vision of a cloth/mummer's dragon

A cloth dragon swayed on poles amidst a cheering crowd. -ACOK, Daenerys IV

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It should be noted that Bran/Bloodraven could influence these battles primarily the Battle of Ice due to the accessible weirwood/heart trees.

In addition to these battles we also have a pretty intense showdown between Brienne/Jamie and Lady Stoneheart/The Brotherhood without Banners, as well as trials in King's Landing, and a showdown with Darkstar should all happen relatively early in the book as well.

TLDR: Just some facts/thoughts on the upcoming four battles that are going to start TWOW off with a pretty intense beginning.