Across Ingushetia, Chechnya, Dagestan and Karabino-Balkaria, Islamist fighters are waging a violent struggle to overthrow their local and federal rulers. Increasingly, they are winning. Friday's apparent bombing of an express train between Moscow and St Petersburg raises the spectre that this conflict in Russia's troublesome Muslim south is again spilling over into Russia's vulnerable European heart. A second deadly attack similar to Friday's explosion would confirm that after a deceptive five-year pause, Chechen terrorism is defiantly back.