In which conflict?
They have been on the same side in many wars, on completely opposing sides in others, and neutral (even through their allies) in others.
Russia
The so called White Armies.
Russia offered support to the Union in the U.S. Civil War because Russia thought the United States was a good counterbalance to the British Empire.
The North
In what ways did the US remain undecided about which side to support in world war 1?
At the side of the Triple Entente, which meant England and France, since Russia was defeated by Germany before the US came.
Western Russia
The US entered WWII when the Japanese bombed pearl harbor in Hawaii.
Britain, France, Russia (late in the war), the US, Canada, and Australia
England, france, Italy, US, Russia (for a while)
US and Uk Allied good guys
Russia was not involved in the US Civil War. A civil war is defined as a war fought between groups which are all from one country.