In brief: The historian’s craft aims to show how our world changes, and who or what has the power to change it. Okay …
In SFF, the world usually changes. It may be saved, destroyed, discovered, overrun by zombies, driven mad by faeries, terraformed, irradiated, touched by strangers, or saved from tyrants, but it changes. Often, the story focuses on characters who shape or initiate the change for good and/or ill: plucky rebels, unlikely saviors, shadowy conspirators, ruthless dictators, the king seeking to rule wisely, the king in exile seeking to return, the faithful followers of the king in exile who make it happen. Live on the page, characters win battles, achieve regime changes, create disruptive technologies, release then battle pathogens, found world-shaping institutions, make passionate arguments in the room where it happens, or are placed by fate in the right place at the right time. If it’s a cozy fantasy, they may even popularize a new kind of bread.
All such stories advance claims about who and what has the power to change the world. Think of a dystopia where the world went bad because of Technology X, versus one where the world went bad because of Villain X, or Corporation X, Political Party X, Global Cataclysm X, Supergenius X, Aristocratic Family X, Religious Leader X—each of these makes a different claim about who and what has power to change our world. A future transformed by a new technology presents a different model of who changes the world if the technology came from one genius inventor, versus the synthesis of two inventers, versus a team of university scientists, versus corporate funding, versus a government lab. A political drama of lords, ladies, and emperors advances the claim that only those at the top have the power to shape history; a drama where the lords and ladies are in conflict with a merchant-class bigwig presents two types of world-shaping power in conflict; a drama which adds an idealist rising from the gutter presents a third; a tale where someone starts in the gutter but enters the elite and uses elite power to actually enact change goes back to only those at the top having power again. A struggling space colony may be saved by rugged space marines, dutiful hereditary lords, the teamwork of the crew, or one special little boy; each option makes a claim about where human power lies, while having the space colony perish despite all efforts makes a claim about human powerlessness.
All such stories are practicing the historian’s craft, not the half that is gathering facts, but the half that is advancing a claim about the causes and secret motions that shape human history.