One of the many books I plan to write is one about aliens invading a medieval nation like England or France but peacefully enough to help one nation wage war against another rather than all nations combining to fight off the alien threat. But would that be wholly realistic?
I know I'm missing something crucial here - I just don't know what it is.
At the first UFO sighting I imagine a pope or an archbishop looking up into the crimson sky and praising the arrival of an auld saint shining brilliantly until the flaming ball smacks the palatial cathedral and seven generations of stonemason back sweat is tossed into the pisspot when all the holy, hand-carved blocks of the archbishopric collapse into dusty heaps. In outrage, knights of the shire ride out to attack "the slimy purple men whose blood is orange and thick like Bertha's marmalade."
The realistic medieval universe the alien invasion will be happening in relishes in its unique affection, yea, affection for detail; 'cus forget attention when shimmering swords are slicing through alien extremities, causing horrendous screams to cascade from hamlet to hamlet - news of a bizarre invasion is spreading! Will the king call off his war to deal with the new threat in his homeland or will he cower like the cat who let its kitten freeze in the cold when there was only enough room in the bolthole for one? How would this alien landing in a generic medieval-land go down?