It was a race to see who could use their advantage first. The Germans attacked first, and under normal conditions could have won, but the England and French knew that if they could hold out until the Americans came they would win the war. So somehow they were able to stop the Germans in spite of the German advantages. Finally the Americans came. We had no secret weapons, or anything that wasn't being used before we arrived,but we had not suffered like the others on both sides for three years. We were full of confidence, and determined to prove our abilities to everyone. The Allies, with the help of the Americans were able to attack.

By convincing the United States to enter the war, the Allies overwhelmed German forces, pushing them to retreat and eventually surrender on November 11, 1918. Germany, Britain, France, Italy and Russia negotiated and signed the Treaty of Versailles on June 28, 1919, formally ending the war.

The Allies 'won' World War I by simply outlasting the Central Powers. Germany was fighting a two front war for most of the conflict, an was bled by a long, grinding, attrition style of trench warfare that took millions of her young men. When the United States entered the war in 1917 on the Allied side, it was fresh, with a huge industrial base already manufacturing war materiel, and a population unbloodied as of yet. There was no way Germany could have competed long term with America allied against her.

Specifically, Germany failed to conquer Paris in the final 1918 offensive, in large part due to the presence of American troops. Germany's economy was bankrupt and teetering, its reserves of manpower exhausted, and it was forced to sue for peace.