What is the Russian Islamic terrorists' beef?

After seeing the carnage of the Boston Marathon bombings up close and personal, my heart goes out to the people of Volgograd, Russia. The recent string of three bombings there left me wondering what the Caucasus Region terrorists want. Has the Russian government left them no choice but to fight, or is it about their “right” to impose their religious beliefs on everyone living in that region of Russia by force of Sharia Law? Is it the Islamic teaching about the reward for giving up your life in a Holy Jihad? What’s driving it? What should Putin do to try and end it?