Germany Russia
after 1) Germany's submarines sunk their ships 2) they intercepted the zimmerman telegraph
Germany had beaten France and other European countries, but not Britain. Britain beat Germany's mighty air force. The Germans and Italians had overrun the Balkan countries. Germany and the Axis allies invaded Russia. Japan was marching all over SE Asia and was beating back the British and Commonwealth troops.
Currently the War on Terror.
a. the US ceased to simply profit from arms sales and became heavily involved in fighting. b. Germany declared war on the US. c. the United Nations was formed. d. the European war became a world war. e. etc etc.
US Civil War and Indian Wars (Frontier Wars).
Please specify which two wars you are talking about.
If you mean the northern states, they fought in the Civil War. Other than that one time, the US has always been united. Any wars which involved the north, involved the entire US. The US has, of course, fought in two world wars and many other wars.
Probably not, the US was the primary supplier of military forces to keep the Persian Gulf sea lanes open (was called the "Tanker Wars" by the press).
How many? You think there has been MORE than two world wars? And in both cases, the US was involved. Honestly, some people.
US Citizens rarely felt a need to join in foreign wars. Germany made it easier for the US to get involved when they declared a policy of unrestricted U-Boat activity.
When John Adams was US president the US was not involved in any wars.