World War 1:
In WW1 Germany, Hungary, Bulgaria, Austria and the Ottoman Empire (these were the central powers) fought agains Russia, Italy, France, Great Britain, Japan, Romania and the United States (these were the allied Powers). This war is also known as the Great War which started in 1914 after the assassination of Archduke Franz Ferdinand. On July 28, 1914 Austria-Hungary declares war on Serbia which started the WW1. The four main causes were imperialism, alliances, nationalism and militarism. This war lasted 4 years where 21 million people died and 21 million where injured. It ended on 11 November 1918 and on June 28, 1919 Germany and the Allied signed the Treaty of Versailles, which formally ended WW1.
World War 2:
In WW2 Germany, Italy and Japan (Axis Power) fought against France Great Britain, the Soviet union, the United States and China (Allied Powers). Hitler attacked Poland on September 1, 1939 (this was an attack that he planned for months). France and Great Britain had guaranteed military support if Poland was attacked by Germany so two days later after Hitler’s strike they declared war. The main causes of it were impact of the Treaty of Versailles following WWI, the worldwide economic depression and the failure of peace efforts. During WW2 Nazy Germany killed around 6 million European Jews (Hitler’s discrimination) - this event is knows as the Holocaust. On 2 September 1945 the USS Missouri in Tokyo Bay, Japan formally surrenders to the Allies, bringing an end to World War II.
Hope this helps. I am just starting year 11 but I picked Geography as GCSE subject so I can’t write that much detail about it Apologies if there are any mistakes - that’s all I can recall from year 9