The First Sparks
Towards the end of the Clone Wars he became increasingly concerned with Chancellor Palpatine’s growing powers, he cultivated a friendship with many members of the Jedi High Council as well as other Senators who had similar concerns.
He visited the Jedi Temple during the Jedi Purge and witnessed clone troopers gunning down a Padawan. During the following months he was able to assist a number of fugitive Jedi.
Organa was involved in operations against the Empire almost from the moment of its inception, mostly by funding and organising small team and giving refuge to individuals fleeing Imperial agents.