World War I resulted in an unprecedented scale of death and destruction, with an estimated 15 to 22 million military and civilian deaths.

The war left a 'lost generation' of young men and caused deep psychological trauma for veterans and societies.

The economic cost of the war was immense, leaving major European nations deeply in debt, particularly to the United States.

The war led to the collapse of four major empires: the German, Austro-Hungarian, Russian, and Ottoman empires.

It also redrew the map of Europe and the Middle East, creating many new nation-states.

The war brought about significant social changes, including accelerating the entry of women into the workforce, which helped advance the cause of women's suffrage.

It fueled the rise of radical ideologies, as the devastation led many to lose faith in pre-war political and social systems.

The spread of the 'Spanish Flu' pandemic in 1918-1919, facilitated by troop movements, killed tens of millions more people worldwide.

The war marked the end of European global dominance and the beginning of the rise of the United States as a world power.

The unresolved issues and resentments from the war, particularly from the Treaty of Versailles, set the stage for World War II.