Short answers, pulled from the story.
Vladimir Lenin issued the Declaration of the Rights of the Peoples of Russia on the 15th of November 1917. This document promised minorities the right to self-determination within the collapsing Russian Empire.
The Soviet government liquidated the Kalmyk ASSR on the 27th of December 1943, the Crimean ASSR on the 23rd of February 1944, and the Checheno-Ingush ASSR on the 7th of March 1944. The Kabardino-Balkar ASSR was renamed the Kabardian ASSR on the 8th of April 1944.
Vladimir Putin began a period of extensive reforms to centralize authority starting from his election on the 26th of March 2000. His administration created federal districts on the 18th of May 2000 and passed laws that gradually terminated power-sharing agreements with regions like Tatarstan and Bashkortostan.
Russia has 22 republics following the annexation of the Autonomous Republic of Crimea which became the Republic of Crimea on the 18th of March 2014. Two additional Ukrainian oblasts were also announced for annexation by Vladimir Putin on the 30th of September 2022.
Republics differ from other federal subjects because they have the right to establish their own official language under Article 68 of the Constitution of Russia. Sakha was granted more control over resources while North Ossetia received more control over defense due to its location in the restive North Caucasus.