World War I was both similar and different from World War II.
Similarities between the two wars: Both wars involved Germany as the cause of and at the heart of the conflict; Both wars ended up involving the nations of France, Belgium, England, Russia, Italy, and the United States; Both wars killed millions of people, devastated vast tracts of countryside, and cost billions of dollars; Both wars were fought in the air, on land, and on sea; In both wars, international alliances were formed between the major world powers, nations rose and fell, disease decimated millions of people, and genocide was rampant; Both wars spawned political upheavals and shifts in balances of power within several nations.
Differences between the two wars: Between the end of World War I and the beginning of World War II, technology improved considerably; Gone were the horses, trench warfare, and biplanes; Military equipment became bigger, faster, more reliable, and more sophisticated; World War II saw more air and sea battles than World War I; Advances had been made in medicine between the two wars so that fewer people died from infected wounds and disease. Whereas World War I was fought mainly in Europe and Asia, World War II was total global warfare. It involved over 100,000,000 soldiers and was considered the "deadliest conflict in human history." (Sommerville, Donald (2008). The Complete Illustrated History of World War Two: An Authoritative Account of the Deadliest Conflict in Human History with Analysis of Decisive Encounters and Landmark Engagements. Lorenz Books. p. 5.); Nuclear power was used for the first time during World War II;
The League of Nations, formed after World War I, was supposed to prevent future wars from happening. But its organization was weak and it lacked the power to enforce its sanctions. Germany, the major offender in the war, was forbidden to join. Then, the Versailles Treaty's terms totally destroyed Germany, paving the way for the rise of the Nazi Regime. The United Nations, on the other hand, was and still is a stronger organization which all nations are encouraged to join. Composed of 143 countries, it remains a means of "keeping the peace" around the world today and has been responsible for much good since its inception in 1945.