Surrounding Oberyn and his escorts were the soldiers of Stannis Baratheon. Having been tipped off by one of Stannis's spies in Highgarden, he was told about the meeting and wanted to use this opportunity to force House Martell to stay out of the war. From his understanding, Dorne was part of the Imperial Union, but not officially as they were like an autonomous region that ruled themselves.
He planned to use Oberyn as a hostage to force the Imperial Union and Dorne to stay out of the war so that he could claim the Iron Throne which was rightfully his. He had already been preparing for a conflict with the Imperial Union and had researched several ways that dragons could be dealt with and how they were dealt with in the past.
He had some of the sellsword companies that he hired, prepared special equipment such Scorpions, poison tipped crossbows and bows, which could weaken a dragon. For some time, he had prepared these weapons and saved them for special use against the dragons. He heard the Imperial Union had hundreds of dragons, even thousands, but he didn't know how true this was.
Spies sent to the Imperial Union territory, never made it back and merchants and other travelers never gave a good estimate. So, he and his commanders opted to just consider that they had at least 200 dragons, at most 400. They prepared nearly 150 Scorpions and made thousands of poison arrows that can be used against the dragons. Other equipment such as trebuchets would also be used.
The group of soldiers surrounded Oberyn and his daughters whom he ordered to surrender. This was their plan from the moment he left Dorne. Maximus knew that Stannis would try to capitalize on this and had ordered the Shadowhand to kill Stannis spies in Highgarden and send a letter prompting him to make a move on Oberyn. Stannis fell for this all too easy and soon enough, he would become yet another piece removed from the board.
He hoped that with Oberyn as a hostage, it would force House Martell to stay out of the war. Even if they did get involved, by the time they could do anything, it would be too late, and he would have claimed the Iron Throne. And if not, then he still had a plan to deal with them. Lots of unknowns for Stannis, but many things he had accounted for as well. Risky yes, but who didn't take risks in this game?
Arriving at Storm's End a few days later, Oberyn, his daughters, and the guards that accompany him were placed into rooms under guard. Not prisoners, but not free either.
Nymeria scowled as she looked out one of the tower's windows. "We should have killed them all," she said bitterly.
Oberyn sighed as he landed on the bed with his hands behind his head. "It wouldn't have changed much," he said. "I thought when some of them drew swords on us, you'd have actually challenged me to see who could kill more." Obara retorted.
"He thinks he can keep us like dogs on a chain. Like he kept Margaery." Oberyn laughed. "Stannis would have more luck chaining the wind." Nymeria turned back from the window. "Shouldn't we do something?"
"We are," Oberyn replied. "We're waiting." Hours later, Stannis met with Oberyn inside his chamber. The guards opened the door and led him in, then posted outside, swords at the ready. Oberyn stretched his arms and stood up.
"I assume you've come to give me a horse and an apology," Oberyn said. Stannis didn't flinch at the sarcasm. "You'll leave soon enough," he said. "But not until I'm certain Dorne won't intervene." Oberyn smiled as if amused by how little Stannis knew the situation.
"Dorne has already intervened, my dear Baratheon," he replied. "You mean your meeting with Renly? He's of no use to us now." "What about your meeting with Lady Tyrell?" Stannis asked sharply. Oberyn tilted his head slightly. "More use than you, it seems." Stannis had already heard from his spies about this union. He knew that Maximus and the Empire were making their move, which was why he had to act fast.
"I know you're aligned with the Imperial Union," Stannis said, "But that can change as quickly as a raven fly. So, I'll ask you once: Will Dorne set aside a continent's squabbles if it means peace with the new King?" Oberyn approached him with his arms crossed and a grin on his face. "What are you offering? Renly made the same proposal, yet here we are in your dungeon."
"Renly offered dreams. I offer certainty," Stannis declared. "A King's word. Once I have the Throne, House Martell will be rewarded as they should have been long ago."
"Words come easy to those who want something," Oberyn said. "And easy promises are just as easily broken." There was nothing Stannis could offer them that the Imperial Union wouldn't already provide for them. Just after a few months, Dorne was filled with trade and things were improving significantly for the common people, increasing House Martell's popularity among not just the common people, but the nobles as well.
The two bickered back and forth, with Oberyn simply playing mind tricks on Stannis. Stannis was not at all pleased with this and left, not able to convince Oberyn to see a different path. After this, he sent a raven to Sunspear, informing Prince Doran that he has his brother, and requesting them to stay out of his affairs. He also sent a raven to Heaven's Reach, warning the Imperial Union to not interfere.
Almost a week later, the news had reached Maximus who already knew about this plan. Arianne walked into his office where she saw the other members of the Imperial Harem and the members of the High Council sitting down.
"Is that the letter" Maximus asked referring to the piece of paper in her hand.
She nodded her head and handed the letter to Olorin, who read it out loud.
"Emperor Maximus, I have Prince Oberyn and his bastard daughters in my custody. They will not be released until I am assured Dorne and the Empire does not interfere in Westeros's affairs. My claim to the Iron Throne is just. If you seek war, you will find it. Stannis of House Baratheon, True King of the Andals, the Rhoynar, and the First Men." His voice trailed off as he smirked at the last line.
Everyone else in the room grinned at just how bold Stannis was. Eonwe practically burst out laughing, not able to contain his laughter. "I haven't laughed like this in a while. Perhaps we could spare this petty King and use him as a court jester of sorts." The rest of the room laughed as it would be quite amusing to see Stannis dressed in a clown suit and forced to tell jokes.
Stannis thought that by capturing Oberyn, it would force them to stay out of the conflict. "Since he wants a war so badly," Maximus stated, "let's give him one." Hela looked excited at the declaration as she had been waiting for some action ever since they went to Qarth and took care of Jaehaerys. She didn't expect it to happen so early but was more than happy to thrust herself into another conflict along with Lilith who was getting bored sitting around.
"We'll make a formal announcement in a week. In the meantime, prepare 5 Legions to send across the sea. One will go to Dragonstone to claim the island and the place where Stannis resides. Another will take the island of Tarth and prepare for an invasion of the Stormlands, while the remaining three will arrive at Sunspear and prepare to march to war with Dorne against Stannis." This was just the start. Now that he was going into Westeros, he wanted to secure as much alliances as he can.
A week later, a formal announcement was made. The Imperial Union declared that Stannis and any Lords sworn to him are now their enemies and they would rescue Prince Oberyn and his daughters, alongside Margaery Tyrell from the Tyranny of Stannis Baratheon who was now called the King of Nothing.
As the war began in the South, the war in the North continued to intensify between the Lannister's and the Starks alongside their allies as they marched further into the Westerlands, burning and pillaging.
Letting them have their way with his land like that angered Tywin more than he thought possible. He moved faster than any of his bannermen expected. Some even doubted his age would let him ride so hard. He left Harrenhal and ordered Gregor Clegane to raid the Riverlands while he marched west with his entire force.
Robb knew that if Tywin was focused on them and not Stannis, then they have already won a manageable victory.
With the power of the reports and Shadowhand agents, Robb was steps ahead of every movement that Tywin made. By the time Tywin's army arrived at Oxcross, they found nothing but burned fields and ruined supplies. The Starks forces were far ahead, raiding Silverhill and Crakehall while Tywin chased rumors of their actual movements.
Once Tywin realized just how big of a grip the Imperials had on everything, he knew that he couldn't risk attacking Renly or Stannis until Robb Stark's men were dealt with. He changed his tactics, pulling west to regroup at Lannisport.
This gave hope to Stannis' supporters who believed they now had a chance to take King's Landing without much resistance. However, with the announcement from the Imperial Union, some doubted that they would be able to take King's Landing and hold the Stormlands against the Imperial invasion which they knew were coming.
A few days after the Imperial announcement and the Imperial Navy had already locked down the Narrow Sea, performing checks on every ship that passed through. It didn't matter if you were a well-known merchant or not, if the Imperials said they were checking your belongings, then there was nothing you could do but nod your head.
Legions had begun to arrive in Dorne while the Dornish still gathered their army which was to be led by Prince Doran himself. The legion that was supposed to attack the island of Tarth was preparing for its naval invasion from Lys. They would be aided by 20 Wyvern riders and 200 members of the Dragon Knights.
Everybody throughout Imperial land began to speak about the Stannis the King of Nothing. Plays were put on showcasing Maximus dragging him through the streets while he shouted about being the true King. Children played jokes on each other saying, "Now you're Stannis."
Everybody in the Imperial Army was prepared for war. Once Maximus announced their conflict with Stannis, many rejoiced and claimed that he would finally bring peace to the continent as he did with Essos.
For Cersei, it was her worst nightmare. The one thing she didn't want the most was happening and there was nothing she could do about it.