During its eight seasons, The CW's Arrow borrowed a lot from the Batman mythology to build its world. From its billionaire vigilante protagonist to using a number of Batman villains, there were a lot of connections to be made between the two. One of those was the League of Assassins and Ra’s Al Ghul, who acted as the “Big Bad” of Season 3.
After that, however, it fell out of focus. So what, exactly, happened to the League of Assassins in the Arrowverse?
WHAT WAS THE LEAGUE OF ASSASSINS?
The League of Assassins is exactly what it sounds like: a league made up of assassins. It was created in 1013AD by Al-Fatih, in reaction to being visited by the Monitor, Mar Novu, and being told that he needed to help keep balance in the world. Al-Fatih took on the name “Ra’s al Ghul,” meaning “Demon’s Head,” a title that is passed on to each leader of the League of Assassins. From there, the league took on its mission: assassinating people who would threaten balance in the world.
There are several characters in the Arrowverse who trained with the League of Assassins, with Damien Darhk, Malcolm Merlyn and Sara Lance being the most prominent. Everyone in the league is trained to near physical perfection with great combat abilities. They also have a strong code of honor and justice, which tends to involve lots of murder if justice is not brought about swiftly.
HOW OLIVER QUEEN DEFEATED RA'S AL GHUL
In Season 3 of Arrow, Oliver Queen got pulled into a conflict with the League of Assassins. They had been at least a little involved the season before, with Nyssa bringing some members of the League to help in the fight against Slade Wilson’s army. Following Sara’s death in early Season 3, however, her killer needed to be brought to justice. While Thea Queen killed Sara under Malcolm’s influence, Oliver took the blame and faced Ra’s in trial by combat. Oliver lost but survived his fall off of the mountain.
When Ra’s al Ghul found out that Oliver survived, he took even more interest and wanted Oliver to be his successor. He brought war to Starling City, first trying to pressure Oliver to join him. Afterward, with Oliver firmly entrenched as his successor, Ra’s pushed Oliver to release the deadly Alpha Omega virus on Starling City.
The plan failed, with Oliver having been working with Ra’s only to betray him. He managed to get the upper hand in a fight, stabbing Ra’s through the chest and killing him. To understand the League better from the inside, Oliver worked closely with Malcolm Merlyn. As payment for his assistance, Oliver gives Malcolm the ring worn by Ra’s al Ghul, putting him nominally in control of the League of Assassins.
HOW THE LEAGUE ENDED
While Arrow mostly moved away from the League of Assassins story at this point, there was still fallout from what happened. Malcolm had the ring of Ra’s al Ghul, but the League split between those who followed him and those who followed Nyssa al Ghul. These factions spent a while at war with each other until it came to a fight between Nyssa and Malcolm. Nyssa won the fight, cutting off Malcolm’s hand in the process, and declared that she had disbanded the League. She melted the ring of Ra’s al Ghul to drive that point home symbolically.
Things didn’t quite end there, as the group loyal to Malcolm continued as the Thanatos Guild for some time. They operated in essentially the same way, even after Malcolm’s death, when his second-in-command, Athena, took over. They were eventually destroyed in Season 8 of Arrow, when Oliver, Thea Queen, and Talia al Ghul fought the remaining members of the Thanatos Guild, who all died in the fight. Thea and Talia then decided to found the “League of Heroes,” believing that the world doesn’t need another League of Assassins. The current state of the League of Heroes is unknown, especially after the multiverse was rebooted during “Crisis on Infinite Earths.”
With the League of Assassins long since disbanded, we’re unlikely to see it again in the Arrowverse. We may see some of its successor, the League of Heroes, but given that Thea and Talia were so tied to Arrow, they may not appear on the other shows. Instead, it’s most likely that the League of Assassins will continue to influence the show through characters who used to be a part of it, rather than being part of the story itself.