In the market, when some of the Smallfolks bought something but the buyer wanted to cheat them, they would tell him, 'Don't be shameless. Are you a Tywin Lannister?'. The matter did not stop here, but it got bigger and bigger; that the joke reached King's Landing.
When Tywin Lannister himself heard it, his face was red from anger and embarrassment since this letter was only meant to be read by Edward. But Edward did not only show it to the nobles in his court, but he also added some remarks and released them to the Smallfolks making Tywin lose his face and House Lannister's dignity.
Since Tywin knew Edward's intention by spreading the content of his letter, he had no other choice but to prepare for war on the southern side which made things difficult for him. Plus, Tywin did not intend to have peace either. He was only trying his luck with that letter.
Tywin himself believed that he had no chances of winning, but he had to protect his family and legacy, even if he had to die.
Tywin did not only send a letter to Edward to solve this matter. Tywin was an old fox and knew exactly how to make use of the time he had. Before he even sent the letter, he had already started recruiting a thirty thousand-man army in Westerlands, in case anything went wrong.
Tywin knew that the negotiation was probably going to fail since he had a long grudge against Edward and the other side was the same, and he wanted to prepare for that situation.
Tywin thought that with the letter he sent, Edward would not get the chance to notice his actions in Westerlands. But he was wrong and so wrong at that because Edward knew what Tywin was like and how he would behave. The moment he got the letter sent by Tywin, he also got what was happening in Westerlands.
Edward waited for another week before taking action because he wanted Tywin to build a big enough army for him to destroy. And at once after that week, Edward sent Jon Clinn to take care of the Lannister's army since he could not go himself. He had a wedding he had to prepare for at this time: and a headache called Axel to take care of, but he was sure that Jon Clinn was enough for this mission.
As for Edward, he had to take care of his emotionless son, who did not change his expression in front of his future wife. But what annoyed Edward the most was the looks on both Margaery and Loras Tyrell, making him think that this was a play done by Olenna.
Edward had dismissed his thought of killing that woman because he thought she was on his side, but he did not trust her since he knew what she did to Joffrey in the other timeline. She might want to do the same to his son, Raymont. Until this moment, Edward was underestimating his elder son's capabilities.
Edward did not know that Raymont had decided to kill Olenna with poison he had acquired from Oberyn Martel himself. The poison was colorless, and it was hard to find and did not kill at once, but it took nearly three months before taking someone's life.
Raymont thought that Olenna was already old enough and she should leave this world in peace. And as Edward had ordered her son's death long ago, Raymont decided to finish his father's work.
Mace Tyrell was on a hunt one day when five mountain lions attacked him killing him with his men. Yeah, that was exactly what Edward prepared for this man since he did not need him anymore.
And Raymont thought that The Reach did not need Olenna and Loras anymore after the wedding, especially after Loras gave his brother that look which made Raymont more furious.
For the next two months, Edward stayed in Storm's Eye while looking at everything from above. The dragons had grown a lot bigger and nearly reached adulthood in the year and a half that passed. Edward wondered why this happened since he watched the show and knew that this size took about four to five years.
But after thinking for some time, Edward thought that this might be due to the sacrifice he made, which accelerated the dragons' growth, or this size was considered young after what he did. Well, killing more than ten thousand men for hatching one dragon egg would sure make this effect. It was not every day that the world lost ten thousand people in one go.
After returning to Storm's Eye, Edward did not forget his other daughter by law and grandson, who did not have their dragons yet. At once, he shipped them with Raymont to Essos to go through the same thing since he could not do such a thing in Westeros. They were supposed to return anytime now where they would participate in the upcoming war.
Anyway, aside from Edward's side, Rob Stark finally fell for the mistakes that he made over time. Edward made Sansa witness everything with her eyes since he did not want her to suspect him of anything, especially Rob's letters that insulted Edward.
Sansa still begged Edward to save him and forgive him for his mistakes, and Edward showed her that he tried and did everything he could, but her brother was the one that did not listen to his words, even after Sansa pleaded to him.
After that, Edward did not stop what happened in the North when Tywin's small army attacked Rob Stark from the South while Walder Frey attacked him from the North. Rob could have probably held his ground for some time against them, but the treason from inside his army fucked everything up.
Roose Bolton had finally reached an agreement with Tywin and Walder and opened the gates of Riverrun for the armies of both sides to swarm inside.
In the end, Rob Stark fell while fighting alone in the great hall of the castle. Even his grand uncle, the blackfish, fell by his side earlier while fighting many men alone, trying to save the young wolf.
As for the Riverrun's heir, he surrendered after seeing that he would die, leaving his nephew and uncle to die alone. He did not care about anyone's life but his. The problem was that he did not get to live long since Edward's assassins took his head, ending the Tully bloodline from the mainline.
With Sansa by his side, Edward could take the North and the Riverlands with ease after that. He only needed time before completing his plans.