Final answer:
World War I was markedly different from previous U.S. wars due to the use of advanced industrial weapons like machine guns, tanks, and poison gas, its global scale involving numerous nations, over 30 million casualties, and its predominantly European theater of combat. The U.S. contributed to the Allies' victory and faced profound resulting changes in political and societal norms.
Step-by-step explanation:
World War I was different from earlier wars the United States had been involved in several significant ways. The weapons used were far more advanced, marking the first fully-industrialized war, which prominently featured machine guns, tanks, poison gas, and airplanes. This led to a shift in how warfare was conducted, with a move towards trench warfare and attrition. Additionally, the war was global, involving nations from around the world rather than being confined to North America or a few overseas territories. The scope of involvement also differed, with a total of over 30 million casualties, indicating a level of destructiveness and death that was unprecedented at the time.
The significance of the United States' declaration of war in 1917 was substantial, as it helped shift the balance in favor of the Allies. American troops had a definitive impact on the Western Front, bolstering the morale and military strength of the Allied forces. In terms of where the fighting took place, WWI was predominantly fought in Europe, contrasting with the more localized conflicts the U.S. had previously engaged in, such as the Spanish-American War or the War of 1812. The scale and nature of World War I brought forth changes to the world's political landscape, influencing post-war peace efforts, societal norms, and ultimately laying the groundwork for future conflicts, such as World War II.