Short answers, pulled from the story.
The North Caucasus is a subregion in Eastern Europe that forms the southernmost portion of Russia. It is bordered by the Sea of Azov and the Black Sea to the west, the Caspian Sea to the east, and the Caucasus Mountains to the south, and it shares land borders with Georgia and Azerbaijan.
The Russian Empire completed its conquest of the North Caucasus by 1864, following the Caucasian War fought against the various regional powers. The annexation of the Mountainous Republic of the Northern Caucasus into the Soviet Union was formalized in January 1921.
Mount Elbrus is the tallest peak in Europe. It is located in the southern part of the North Caucasus region.
The North Caucasus is predominantly Sunni Muslim. The eastern portion, including Chechnya, Dagestan, and Ingushetia, is dominated by Sufism, while the western republics maintain traditions of paganism intertwined with Islam. The Ossetians and Abkhazians are exceptions to the Muslim majority.
FSB Director Alexander Bortnikov declared the insurgency over on the 19th of December 2017, announcing the final elimination of the insurgent underground. Counter-terrorism operations in the region continued after that declaration.
Between the 1850s and World War I, roughly a million North Caucasian Muslims, including Circassians, Chechens, Ingush, and Ossetians, became refugees in the Ottoman Empire. The Ottoman government resettled them across territories that now include Turkey, Syria, Jordan, Lebanon, Israel, Iraq, and several European countries.