Answer:
1.) 20 millions peoples died in WW1
2.) Serbia
3.) central power ===Germany, Austria-Hungary, Bulgaria and the Ottoman Empire
allies power === Britain, France, Russia, and the United States.
4.)By that time, the German leadership believed that the United States was effectively acting as a belligerent in the conflict, given actions such as Lend-Lease of supplies to Britain to sustain their war effort, President Roosevelt's public statements, the deployment of American soldiers and Marines to Iceland, and U.S.
5.) The note revealed a plan to renew unrestricted submarine warfare and to form an alliance with Mexico and Japan if the United States declared war on Germany. The message was intercepted by the British and passed on to the United States; its publication caused outrage and contributed to the U.S. entry into World War I.
6.) The Treaty of Versailles Punished Defeated Germany With These Provisions. Some disarmed the German military, while others stripped the defeated nation of territory, population and economic resources, and forced it to admit responsibility for the war and agree to pay reparations.