Russian intervention in Ukraine
As a response to Euromaidan and pro-Russian unrests in Eastern Ukraine, Russia deployed its troops in Donbass region to support Novorossiya's Resistance. This act was considered as an act of hostility by Ukraine, that immediately declared war to Russia, and with overwhelming power invaded Crimea and Eastern Ukraine. In september 2015, United States invited Ukraine to join NATO, which caused whole NATO coming to war with Russia. Russia, unable to resist the armies of both superpowers, fell within four months.
After the retreat of Russian Army from territories controlled by NATO, NATO created a provisional puppet state of Western Russia. As a respond, former Russian government has declared an asian part of Russia as a territory of Russian Federation. Both sides achieved a bitter peace for a six months.
After the disintegration of Russia, more than 70% civilians available for service joined the Army of Russian Federation. In 2015, Russian Army had more than 7,000,000 active men. Due the information embargo imposed on NATO, the West didn't know about its strength.
Counterattack and reunification
In February 2015, Russia declared war to the West and attacked the American cores in the occupied territory. After retaking Volgograd, NATO forces started to retreat to Ukrainian borders. In June, Russia has liberated Moscow, and 2 months later, Russia controlled Saint Petersburg and Rostov-on-Don. After Russia liberated 80% of its former territory, USA in the name of NATO offered peace to Russia, which was refused. After that, Russian Military Staff decided to get revenge - and started the Reprisal War.