I ask why we should stand on ceremony, our OP may well be as clueless as the rest of us in terms of the terrorist's grievances against Russia. But its pretty clearly a terrorist attack and not some accidental railroad accident. And I wonder how long it will be before multiple groups claim they done it.
Russia and multiple European countries have a long and rich history of terrorists attacks, to some extent they earned them, so how do you comment other than to post the news that a significant attack occurred?
My other comment is that the USA lost its terrorist attack virginity in 911, and as the USA increasingly engages itself in fruitless quagmires, why should we not expect to be raped again?