"Kar Kaballa" is a 1969 science-fantasy novel by George H Smith, published as one half of an Ace Double, with the other side being Tower of the Medusa by Lin Carter. It is 140 pages long, and (like the other half) combines science-fiction and fantasy with an adventure story.
Many Ace Doubles have fanciful plots that it takes a while to understand. "Kar Kaballa" starts with an American visiting Europe, trying to convince the people there that Russia is imminently going to invade, and with the Europeans scoffing at him for being alarmist: all those myths about Russia are just scare tactics, and Russia is too good of a source of raw materials. That is the plot, but the names have been changed: this is a fantasy world, where the US is Vineland, Britain and Europe are Avallone, and the Russians are Gog. Our hero is Dylan McBridge, a kilted Scotsman from Vineland, who knows the truth about the Gogs and the chaos deity they worship. But no one seems to believe him, until he bumps into a man who turns out to be from our world. There is a mystical gate between the worlds, and it is the same year in both: 1895, with similar levels of technology, although Avallone has some steam punk things going on, like airships with artillery. They don't have Gatling Guns though, and that is what the stranger is here to deliver. Can McBridge convince the nobility of Avallone to take the threat seriously, and arm them with modern weaponry before the Goggish hordes invade?
Many answers to these questions are clear from real life.
But taking away that "real life" thing, this is an adventure story that combines aspects of Conan the Barbarian, the Cthulu Mythos and steampunk (even though it predates steampunk). The science aspect doesn't really make sense---we are never really given an explanation of how the worlds are connected. But of course, we don't need one. And even though the book has a gigantic war and a struggle between cosmic forces, it also manages to mix in a love triangle, with Dylan meeting Clarinda MacTague, the rambunctious priestess of a Celtic fertility goddess. And while MacTague is described in detail as having the figure and shamelessness of a fertility goddess, by the end of the book we have determined that she is chaste and our romance is sealed with a kiss.
This is a fun, and creative, if somewhat predictable, fantasy adventure novel, and I will keep reading books like this as long as I have them.