Destroy is more general, it covers wrecking, ruining and killing. Demolish tends to apply to very large things: "When they demolished the building, several anthills were destroyed." Demolished is also the word more often used metaphorically: - He demolished two heaping plates of food, eating like he hadn't seen food for days. - He destroyed a plate of food by throwing it against the wall so hard it broke the plate.

What's (the) difference between demolish and destroy? They're pretty much synonymous in my ears, though demolish might connotate a building or construction being destroyed, while destroyed is more general. Though, honestly, they're so similar that in the vast majority of cases they can be used interchangeably.