Barsoom influenced Flash Gordon

Alex Raymond's strip began in 1934 as King Features' answer to Buck Rogers, and the template it reached for was Burroughs's:

• An Earthman stranded on an alien world who becomes its champion
• A princess of that world as the romantic centre
• Warring races, court intrigue and a tyrant, all settled by swordplay rather than by the advanced technology the setting obviously has

That last point is the signature of the form. Planetary romance keeps the sword in a world with airships, and Burroughs is where the convention comes from. Flash Gordon then carries it forward to Lucas, which the graph already holds.