5. The Thirty Years War: 1618-1648
Clearly, the length of this war could cause mass amounts of death and destruction, but that doesn’t make the conclusion any less devastating. Another war waged over religion, this armed conflict that took place all over Central Europe arose between Catholic and Protestant states, after the fragmentation of the Holy Roman Empire.
As the years went on, the war only continued to deepen and grow, with the majority of the greater powers of Europe stepping into the fray. While the death toll has never been able to be accurately pinned down, estimates regarding the death toll vary as widely as three million to 11.5 million (though many have agreed on eight million as the most probable number).
4. World War One: 1914-1918
Undoubtedly the World Wars would leave behind the most damage. WWI was a global event that began in Europe and expanded outwards, gaining support from all of the major economic powers. They banded together in two separate alliances, the Allies and the Central Powers, and countless battles ensued through the use of trench warfare.
The death toll rounded out to about 18 million, 11 million of which were in the military and another seven million civilians. Whereas many earlier wars had high death rates due to famine and disease, WWI saw many of its deceased come from the battlefield.