Quick questions on Why the Allies won the First World War explained: N(A)-Level History

The single most important change was the entry of the United States into the war in 1917. The United States was a huge, wealthy and growing country that had stayed out of the fighting. Germany's use of submarine warfare to sink ships, including ships carrying American passengers and goods, helped push the United States to join the Allies. American entry brought fresh soldiers, vast amounts of money, food and equipment, and a great boost to Allied morale.

For most of the war the British navy controlled the seas and used a naval blockade to cut off Germany from overseas trade. This meant Germany could not easily import food, fuel and raw materials. Over time the blockade caused serious shortages inside Germany. Ordinary people went hungry, factories ran short of materials, and discontent grew on the home front.

By early 1918 Germany knew that American troops would soon arrive in huge numbers. So it launched a massive offensive in the spring of 1918, gambling everything on a knockout blow before the Americans were ready. At first the attack made big gains, but it could not be sustained. The German troops were exhausted, supplies could not keep up, and the offensive ran out of strength.

To reach a judgement, think about how the reasons connect. The blockade weakened Germany slowly over years. The entry of the United States added overwhelming new strength to the Allies. Germany's failed 1918 gamble used up its last reserves at the worst possible moment.