Why did the World War 1 cost so much?

World War I was extraordinarily costly due to several factors, including the extensive mobilization of troops and resources, advanced military technology, and the scale of destruction across multiple countries. The war required massive expenditures on weapons, ammunition, and infrastructure, leading to national debts that burdened economies for years. Additionally, the prolonged nature of the conflict and the involvement of numerous nations further escalated the financial toll, resulting in significant human and material losses.