How did Germany break the rules in World War 1?

Germany broke the rules of World War I primarily through its use of unrestricted submarine warfare, which violated the principles of neutral shipping rights. The sinking of civilian ships, including the Lusitania, led to international outrage and contributed to the United States entering the war. Additionally, Germany's use of chemical weapons and its aggressive military strategies, such as the invasion of Belgium, also violated established wartime conventions. These actions ultimately undermined Germany's position and credibility in the conflict.