It was the British who won WW1 due to a Naval Blockade on Germany meaning no food got to the population. The US entered in the summer of 1918 although a year before they declared war on germany ( were ships so slow it took a year to travel 3000miles ). The war ended on 11th Novermber 1918 at 11am. The British had developed tanks before the US came in and had pushed the Germans back. Are you taught that you won WW1 or do you have an accurate teaching of it?
We will accept WW2 was highly down to you though but not WW1. That was Britain as we were the biggest superpower at the time and still were after.