One of history’s deadliest conflicts in proportional terms is the little known War of the Triple Alliance, also known as the Paraguayan War, fought from 1864 to 1870 between Paraguay and an alliance of Argentina, the Empire of Brazil, and Uruguay.
Resulting in over 400,000 deaths in total, it is Latin America’s deadliest war, though it caused the most suffering for Paraguay: in addition to losing a large chunk of its most resource-rich territory, the country may have lost 60 to 90 percent of its total population, including 70-90 percent of males.
The stripped area represents pre-war territory that was subsequently annexed by Argentina and Brazil. Source: GlobalSecurity.org
Most of these horrific losses were due to war-related outbreaks of disease, as well as to the desperate measures taken by Paraguay’s dictator, Francisco Solano López, who continued to lead a guerrilla campaign that involved the conscription of boys and a scored earth policy.
Note that there is still some dispute as to the exact casualty and fatality numbers, with some scholars suggesting it may not have been higher than 23 percent — which would nonetheless still put the Paraguayan War as among the deadliest in the world, and certainly the Western Hemisphere.
Sarvodaya 