Abandonment of Dragonstone

The Abandonment of Dragonstone was an event during the War of the Five Kings, leading into the first action of Daenerys Targaryen's invasion of Westeros when she landed on Dragonstone.

History
Stannis Baratheon left his main base at Dragonstone with his entire army to save the Night's Watch at the Battle of Castle Black.

Stannis totally abandoned the castle, taking every last man with him to aid his campaign in the North.

Meanwhile, House Lannister in King's Landing made no attempt to capture the now totally abandoned castle, for the next three full years during the reign of King Tommen Baratheon. The Lannisters were aware that the castle was utterly undefended - though Dragonstone is a vitally important island fortress commanding the naval approach to the capital city through Blackwater Bay. After Tommen's death and Cersei's seizure of power, Cersei asked Jaime Lannister where Daenerys Targaryen was most likely to land first when she began her invasion of Westeros. Jaime correctly assessed that she would probably try to take Dragonstone first, as it has good deep water ports for her fleet, Daenerys was born there, and Stannis left the castle abandoned so she wouldn't face any resistance. Neither Jaime nor Cersei suggest rushing Lannister soldiers to the abandoned castle to defend it from Daenerys's landing.

When Euron Greyjoy came to King's Landing with his fleet to propose a marriage-alliance with now-Ruling Queen Cersei Lannister, he made no attempt to capture the empty fortress, despite passing it twice as he entered then left Blackwater Bay.

Ultimately, Daenerys lands her fleet at Dragonstone without opposition. She and her followers enter Dragonstone castle, and she assumes control, to begin planning her invasion of the rest of Westeros.

In the books
Daenerys Targaryen hasn't returned to Westeros yet as of the most recent book in the A Song of Ice and Fire series.


 * The TV series stated in the Season 7 premiere that when Stannis left with his army for the Wall, at the end of Season 4, he left Dragonstone completely abandoned, and that it remained abandoned up until Season 7 - three years later in the storyline - this is absurd, and has no precedent in the novels whatsoever. There is no reason why the Lannisters wouldn't try to capture the abandoned castle.  When Daenerys arrives the castle is indeed abandoned, she faces no resistance, and she pulls down an old Stannis banner which no one has removed since he left.
 * In the books, Stannis took most of his army by ship to the Wall for the Battle of Castle Black, but he left a small skeleton force garrison behind - because Stannis hopes to eventually retake all of the Seven Kingdoms, and it wouldn't make sense to voluntarily abandon the defense of one of the strongest castles in Westeros. Dragonstone was constructed with lost Valyrian architectural techniques and is defensively quite formidable, so even a token defensive force can hold it against large armies.
 * Given how strong the fortress is even this small garrison was enough to deter a direct attack by the Lannisters: as a result much of the remaining Lannister/Tyrell fleet was pinned down encircling and besieging Dragonstone, trying to wait them out through starvation over time. This prevented the Lannisters or Tyrells from dealing with the rise of Euron Greyjoy on the west coast. Loras Tyrell has come up with the idea to force a quick end to the siege by storming the castle, stating that he can conquer the castle within two weeks; Cersei agrees, in hopes he will die in the fighting. Loras takes the castle, but with heavy and unnecessary losses due to his rash nature, and after fighting through many defenders despite taking numerous wounds, he was doused with boiling oil and left barely clinging to life. Cersei then needlessly gloated to Margaery about Loras, breaking down the already fragile Lannister-Tyrell alliance. The TV series omitted all of this and just had Loras burn to death in the Destruction of the Great Sept of Baelor (in either version, he apparently burns to death - though there is some slim chance he might in fact survive in the books). As a result, as of the most current novel Dragonstone is weakly held by a remaining Lannister force after the siege.
 * Even if Stannis felt he needed to take every man he had to the Wall to focus on the campaign there...there is no plausible reason that the Lannisters would simply leave it abandoned for three years and make no attempt to retake an empty castle. Particularly because Dragonstone directly controls the sea approaches to King's Landing, across the Gullet at the entrance of Blackwater Bay.  In the second novel, Stannis controls most of the former Royal Fleet, so his possession of Dragonstone allows him to enforce a naval blockade on the capital - which combined with the Riverlands and Reach no longer sending food shipments, leads to food riots).
 * This has zero precedent at any point in the history of Westeros: even if Dragonstone doesn't control the sea approach to the capital city - which it does - but if it were a more isolated castle like Storm's End or The Eyrie, no one in the history of Westeros would make no attempt to occupy a totally abandoned castle...no attempt in three years of story time.
 * Note that Theon Greyjoy managed to take and briefly hold Winterfell with a force of only 20 men. In the books, even a force of a mere 300 men can hold Dragonstone against armies in the thousands.
 * Even within the episode, Jaime himself observes that Stannis abandoned the castle, the Lannisters are aware of this, it is relatively nearby, and he says that it's the most likely target for Daenerys Targaryen's initial landing...yet he doesn't make any attempt to suggest that they should rush even a small force of Lannister soldiers to the castle so they can defend it against her attack. Even if they hope to defeat Daenerys, they would eventually have to retake Dragonstone castle, losing thousands of men in the process, when they could have just sent a hundred or so guards there ahead of time.
 * Euron Greyjoy's fleet had to directly pass abandoned Dragonstone, both coming and going to King's Landing. This is also blatantly obvious given that Jaime is standing on a large map at the time, visibly showing that any ship approaching King's Landing has to pass Dragonstone.  Yet the TV show presents that Euron wouldn't think to capture the island, perhaps as a gift for Cersei.
 * Even if the storylines are out of synch, and Daenerys lands on Dragonstone before Euron arrives...then Daenerys's fleets would be based at Dragonstone, and attempt to stop Euron's fleet from reaching King's Landing. As presented by the episode, Daenerys simply hadn't reached Dragonstone yet, and Euron ignored capturing one of the strongest castles in Westeros even though it was empty.
 * Euron's fleet would have to sail past the Tyrells' home fleets to get all the way to King's Landing. This is comparable to when, in Season 4, the TV show had Yara Greyjoy circumnavigate the entire continent of Westeros, to sail from the Iron Islands around to The Dreadfort on the northeast side (the equivalent distance of sailing from Peru to Venezuela, the long way by sailing south around Argentina).  Yara could plausibly have made a portage at the Neck, as Moat Cailin was held by the ironborn at the time, but that's just fan theorization).  Even Yara could plausibly slip past enemy fleets as one ship - Euron's large fleet would have been blocked.
 * The TV show could, plausibly, have just said that Euron reached King's Landing by land, or on one ship, but apparently it wanted the big visual of Euron sailing a large fleet into King's Landing - without considering why Euron wouldn't split off a few ships to take Dragonstone.
 * Ultimately, even if Euron's arrival isn't considered, there is no plausible reason why the Lannisters wouldn't retake an empty Dragonstone castle in three years. Or even send a few fishing boats' worth of men to take it.  The TV series cut out Loras's major subplot on Dragonstone and didn't want to expend more time explaining what happened to it.  The TV writers didn't even want to expend time explaining in dialogue something like that off-screen, without Loras, the Lannisters retook the island from a token defensive force left by Stannis, but then the Lannister forces holding Dragonstone were overwhelmed by Daenerys's massive army when taken by surprise.  This doesn't particularly affect long-running storylines that will come after this now that Daenerys holds Dragonstone.
 * The fate of the Bald Dragonstone servant remains unknown. He may have simply abandoned the castle as well, rather than hold it against the Lannisters - or, he may have correctly anticipated that in defiance of all historical precedent, the Lannisers would make no attempt to capture an abandoned castle.