World War 1
Causes of the war
World War 1 seems like Germany just had it out for everyone. But it was really the assassination of Archduke Ferdinand. This caused Austria-Turkey to become enraged and ask their allies to help them wipe out Serbia. After this many other countries got involved and all war broke loose...literally
The Triple Entente vs. the Central Powers. Not only were there new guns, but there were also new weapons such as tanks and chemical warfare. It was an absolute slaughter on the battlefield. Soldiers had to use Trench Warfare for cover and surprise shots. After all of this, soldiers had to have masks to protect themselves from mustard gas.