Americans were involved in the war by aiding the Allied powers. Ex. Great Britain. They would manufacture products and American sailors would sail over to Britain to deliver supplies. American submarines and cargo ships being sunk by Germany was part of America's growing annoyance with the war.
In its simplest form the domain is all the values that go into a function, and the range is all the values that come out. But in fact they are very important in defining a function.
