World war one was started by the arch duke Franz Ferdinand and his wife being assassinated by the black watch. People started blaming each other until Serbia and Austria declared war on each other and then everyone got involved because of treaties and alliances
World War one was supposed to be the war to end all wars but it actually had problems that just lead up to world war 2. Most of the technology around that time made for a lot of problems, also weapons were advancing at a rapid rate. Three examples of these weapons were grenades, flamethrowers, and U-boats. While many other weapons were used in world war one, these three were among the most destructive of them all.