They remained successful while the Russians were occupied with the Crimean War, but the Russians used larger forces in their later campaigns, and, when Shāmil was captured in 1859, many of his followers migrated to Armenia. The Terek River remained a defensive frontier until the 1860s. The constant skirmishes of Chechens and Russians along the Terek form the background to Leo Tolstoy’s novel The Cossacks.