What were the similarities between WWI and WWII?
There are at least three major similarities.
First, both wars were caused by the efforts of some countries to change the international order and the efforts of other countries to prevent that. For example, Germany wanted more power for itself before both wars and other countries wanted to keep it from having power.
Second, both wars were "total wars" that were won by the side that could manufacture the most weapons.
Finally, both were wars that ended with victories for the countries that had dominated the world order before the war. In other words, the insurgent countries lost both wars.
There were many similarities between World War I and World War II. One similarity was the causes of each war. In both world wars, imperialism, nationalism, and militarism led to the outbreak of war. Countries like Germany, Japan, and Italy wanted more land and resources. Since most of the desirable land was already taken, they had to get it by aggressive actions or by going to war. These countries also believed their way of life, military, and political system were superior to any of these concepts in other countries. Thus, they weren’t afraid of war because they believed they would win. Additionally, these countries began to build up their military. They had plans to use their military.
Another similarity of World War I and World War II is the role the United States played in each war. The United States didn’t join either war when they first started. In World War I, we joined the war after Germany resumed its policy of sinking our merchant ships without warning. In World War II, we joined the war after Japan attacked us at Pearl Harbor. In both wars, we helped the Allies to victory.
A finally similarity is that in both World War I and World War II we were more sympathetic to the Allies than to the Central Powers and Axis Powers. Our language and government were similar to that of Great Britain. In World War I, we were doing more trade with Great Britain and France than with Germany and Austria-Hungary before we joined the war. The Germans used submarines to try to reduce this trade. In World War II, Germany also used submarines to impact our trade with Great Britain. The United States was doing everything it could before we joined the war to help Great Britain. Policies like Destroyers for Bases, the Lend-Lease Act, and establishing a hemispheric defense zone were ways we tried to help Great Britain before we joined the war. There were many similarities between World War I and World War II.
Both WWI and WWII had some similar causes: nationalism, imperialism, alliances, and militarism. In WWI, tensions rose between European nations over imperial territories in Africa and elsewhere in the world. The idea of nationalism, pride or love for one's country, propelled Europeans to search for more land in order to honor their country. Different pacts and alliances made certain that if two countries were to go to war, a bunch of other countries must join in (making it a world war as opposed to a war between two countries) and an increase in weapons from the industrial revolution made militarism a serious threat. In WWII, German nationalism was rising after its defeat and humiliation in the wake of the Treaty of Versailles. Germany also wanted more land for itself, and invaded surrounding territory in Czechoslovakia and Poland to obtain it. There were more alliances formed in WWII, and militarism was increasing globally as well. In other words, both wars saw countries trying to upset the balance of power in Europe.
Another similarity between WWI and WWII was the use of German u-boats and the use of new weapons never before used.
Additionally, both wars saw a heavy use of propaganda to support war efforts, both at home and in other countries in Europe.