World War I (1914 - 1918) was undoubtedly one of the greatest catastrophes of the 20th century. Estimates suggest that approximately 15 - 22 million people died, including both military personnel and civilians. Millions of soldiers lost their lives in trenches, under artillery fire, and during massive military offensives.

However, history has witnessed other extraordinarily deadly conflicts. For example, the Mongol conquests of the 13th and 14th centuries and the Taiping Rebellion in 19th-century

China are estimated to have claimed tens of millions of lives. The exact death tolls are much harder to establish, making it impossible to rank World War I definitively as the second-deadliest conflict in history.

The main difference between the two world wars lies not only in the number of casualties but also in the scale of destruction. World War I reshaped Europe's political map and led to the collapse of several empires. World War II engulfed an even larger part of the planet, involved the Holocaust, mass killings of civilians, and the use of atomic weapons.

Conclusion: World War I was one of the deadliest conflicts in human history, but it cannot be unconditionally ranked second in terms of casualties. Historical rankings depend on which conflicts are compared and which deaths are included.