Why did ISIS attack Russia?

Sergei Migdal, a military analyst and erstwhile Israeli police officer who is referred to as Currenttime.tv suggested that the attack could actually have organized the Afghan wing of ISIS. In his opinion, this is due to the fact that **after the withdrawal of US and Western troops from Afghanistan, Russia established friendly relations with the Taliban**. Although Taliban was officially banned in Russia as a terrorist organization, after taking Kabul, the Taliban were invited, among others, to the Petersburg economical Forum.