Lewiatan by Scott Westerfeld

Set against the backdrop of an alternate World War I, this thrilling tale follows the intertwined destinies of two young protagonists from opposing sides of the conflict. One is a prince on the run after the assassination of his parents, while the other is a daring girl disguised as a boy to join the air force. As they navigate a world divided between the Clankers, who rely on steam-powered machinery, and the Darwinists, who harness genetically engineered creatures, they must overcome their differences and work together to survive the chaos of war. Their journey is filled with adventure, intrigue, and the exploration of themes such as identity, loyalty, and the clash between technology and nature.