in World War One the US announced its nuetrality but a telegram between Germany and Mexico asking Mexico to fight against the US and several public ships being sunk the US declared war they sent men...
The US saved the United Kingdom during WW1 (and again in WW2. The US saved the UK; via US manpower, US weapons, US fuel, US food, US merchant ships, US ammunition, US medical supplies, etc.
The US forces and the Allied Forces fought back ferociously and they were victorious. See the links below for the entire story of the victory of the Allied forces and the surrendering the Japanese...