Scott Westerfeld, "Behemoth (Leviathan)"

If Leviathan was setting up World War One with mechs and genetically engineered creatures, Behemoth was expanding upon the political ramifications. The book primarily centers on the political machinations between the Darwinist English and the Clanker Germans vying for the favor of the kind-of-sort-of Clanker Ottoman Turks in Istanbul. In the middle of this is Alek, son of the nobles whose assassination lit off the whole mess, and Deryn/Dylan the crossdressing girl serving on the English airship Leviathan and crushing over Alek.