The Book of Ruin by W.G. Hladky

WINNER OF THE 2020 INDIEREADER DISCOVERY AWARD FOR SCIENCE FICTION. The sun batters earth with endless solar storms. The world enters a Dark Age. Descendants of American soldiers in Germania defend the last NATO outpost. NATO sends Senior Chief Loveboy Weir and his ranger team to investigate mysterious raiders called the Vucari. Traveling in anti-gravity vessels, they visit the beautiful city-state of New Reykjavik and mountains where Kazaks use giant eagles to hunt enemies. They also journey to the City of Ghost that spews poison and to a floating monastery where monks protect the Book of Ruin. They eventually encounter Prince Vladimir, the Vucari warlord, who claims to want peace but decimates any population that resists him. Weir struggles to convince NATO not to trust Vladimir. While politicians make backroom deals to appease Vladimir, Weir prepares for a war he fears is coming.