If you have ever heard the concept of "An enemy of my enemy is my friend" the reason why the US and Russia were fighting on the same side will make perfect sense. We and Russia were fighting against what seemed to be a more imminent threat, Nazi Germany. This brought them together for a common interest.
Russia
During the war with Poland in our serbian history
war world 1
They were used as code breakers to aid the Americans during the war.
the medic
why
Russia
During World War I, Belgium's primary allies were the Entente Powers, which included France, the United Kingdom, Russia, and later Italy and the United States. Belgium was invaded by Germany in 1914, prompting the UK to declare war on Germany due to its commitment to defending Belgian neutrality. Throughout the war, Belgium received support from these allies in terms of military aid and resources.
Both sides in the Spanish Civil War received aid from outside Spain. France did not receive aid during or as a result of the Spanish Civil War.
Andre Vulliet has written: 'Preliminary report of the War Prisoners Aid, Young Men's Christian Associations during World War II' -- subject(s): Prisoners and prisons, War work, World Alliance of YMCAs, World Alliance of YMCAs. War Prisoners' Aid, World War, 1939-1945, Young Men's Christian associations
After archduke Ferdinand was assassinated, Austria Hungary declared war on Serbia. Russia then came to Serbia's aid because of an alliance and declared war on Austria Hungary. Germany declared war on Russia because of its alliance with Austria Hungary. Britain declared war on Germany because of its alliance with Russia. Other countries such as France and the Ottoman Empire soon chose sides and World War 1 began
Austria-Hungary believed that Russia would not come to the aid of their ally Serbia because they thought Russia was preoccupied with internal issues and would not risk a war with Austria-Hungary.