The military differences between World War I and World War II was that the former armed conflict was a static kind of warfare, in which, due to the massive use of machine guns and modern cannons and howitzers, armies were forced to dig complex trench systems and bunkers to protect their men from lethal artillery barrages and, thus, avoid high casualty rates; also, these modern automatic weapons, which were the byproducts of the Second Industrial Revolution, meant the end of cavalry, forcing army generals to use the large amount of available mounted soldiers as infantry units. To conquer ground, generals ordered futile infantry attacks on well-protected enemy positions that cost thousands of lives in one single assault only to gain perhaps a mere three hundred yards, to be thrown back again by an enemy counter-attack. In order to break the static nature of World War I and get the infantry out of the trenches to effectively conquer enemy-held territory, the military developed the first tanks, which, not only provided protection against machine gun fire, but also overcame the battlefield obstacles, such as barbed wire and trenches. However, these tanks were still primitive and, as a result, the advance was still slow and costly. Furthermore, during the Great War, military aviation was in a rudimentary stage and its effective use was limited to reconnaissance and dog fights against enemy pilots in the sky as aircraft consisted of slow and flimsy biplanes and triplanes. Since cavalry no longer functioned and armored vehicles and aviation were still in diapers, I dare to say the infantry and artillery were the queens of the battlefields in World War I.
In contrasts, World War II was a dynamic and mobile warfare, owing to the introduction of Blitzkrieg by the Germans; it was also multi-front, as it was widely fought, with several theater of operations. Although new and devastating weapons were used for the first time, neither sides employed chemicals, such as mustard gas, as in the Great War. The Germans were able to successfully carry out the Blitzkrieg concept thanks to the availability of faster tanks, with accurate and powerful guns, and, above all, the modern attack aircraft. The German Junkers Ju 87 “Stuka” was the Wehrmacht devastating flying artillery that provided timely support to spearhead mechanized infantry units. Tanks became the new, armored modern cavalry and the Germans were the first to use them in single concentrated armored units (not mixed with the infantry). The attack aircraft were used in synchronicity with tanks divisions, which were employed to punch holes in the enemy front lines and thus be able to encircle and trap enemy units. Perhaps, the only battle that was static in this war, as it was fought for months, was the Battle of Stalingrad, but it was an urban type of warfare, which is different from a trench one. World War II was also characterized by massive use of medium and heavy bombers to destroy factories and cities with the objectives of crippling the enemy industrial capacity and demoralizing the civilian populations; this is called carpet bombing and was intensive and extensively used by the Allies, employing incendiary bombs to destroy civilian buildings. The fire bombings of Dresden, Hamburg, and Tokyo are examples of carpet bombing. World War II was also the first armed conflict in the history of mankind in which more civilians died than military, due the Jewish Holocaust, carpet bombing, and the first use of nuclear weapons.