The Long War

War has come to the Long Earth. . . .
Humankind has spread across the new worlds opened by explorers Joshua and Lobsang a mere decade ago. Now "civilization" flourishes, and airships link the multiple Earths. A new America christening itself "Valhalla" has emerged more than a million steps from the original Datum Earth. Like the American revolutionaries of old, the Valhallans resent being controlled from afar. And in the wake of humankind's advance, the trolls— graceful, hive-mind humanoids whose song has suffused the Long Earth— are beginning to fall silent . . . and disappear.
Joshua, now married and a father, is summoned by Lobsang. It seems he alone can confront the perfect storm of crises that could plunge all of the Long Earth into war— a war unlike any that has come before.