Russia was a vast Pre-H nation-state straddling the continents of Europe and Asia. Many times the size of the United States, but less populous, Russia fell under the control of a dictatorial regime known as the Union of Socialist Soviet Republics (USSR) in AD 1917. Although allied with the United States in World War II, the two countries' ideologicial differences saw a 'cold war' of intrigue and brinkmanship develop over the following half-century, during which time both countries developed immense stockpiles of nuclear weapons.
The USSR collapsed in 1990 and the USA lent its former enemy aid and support in reestablishing its economy and a new, more democratic government. However, tensions between the former adversaries did flare up from time to time, and both countries maintained strong nuclear arsenals, albeit at a reduced level from their late-20th Century heyday.
On 17 November 2015, the United States engaged in a brief conflict with other nuclear powers. Russia is the only other country mentioned in the historical archives. The exchange of missiles lasted just a few hours but totally destroyed human civilisation, levelling most of the world's major population centres. Between the deaths in the war and in the nuclear winter that followed, at least 95% of the human race was exterminated.
A small number of Americans survived in deep underground bunkers to eventually found the Amtrak Federation. The status of Russia in the closing years of the 30th Century and whether there are any survivors there is unknown.