League of Assassins (New Earth-One)

Founding
The League of Assassins was founded by the immortal Ra's al Ghul during the Third Crusade in the late 12th century, where they were instrumental in the defending against the European Crusaders. Ra's al Ghul himself claimed that he sent one of his assassins to Poison Pope Urban III, which may or may not be true.

The League spent most its early days defending the early Muslim lands during the Crusades and would continue to do this in till the Crusades ended.

Post-Crusades
After the Crusades ended, the League began to fade into the shadows working as silent assassins for hire.

During this time as well, Ra's al Ghul began to grow increasingly paranoid about his enemies discovering and destroying his secret Lazarus Pit that granted his immortality and strength. in order to quell his fears, Ra's al Ghul decide to use a map that he found in the cavern of his Lazarus Pit to find more Pits around the world. Ra's would take a party of his best assassins in search of more Pits and would leave his father only known as Sensei in-charge in till his return.

The League would grow under Sensei watch, expanding through most of the Middle East during the 14th century and would prosper in secret.

Ra's al Ghul's Return
Later in the 14th century Ra's al Ghul would return to his home in the Middle East telling his father that he discovered multiple Pits throughout Asia and had created new branches of the League of Assassins in Asia to protect his newly discovered Pits.