The annals of military history are full of examples in which insect-borne disease has played a crucial role in the outcome of a battle or a war:

In 1346, an army of Tartars besieged the city of Caffa on the Black Sea.  When an outbreak of plague developed among the Tartars, they hurled their dead over the city walls until the citizens surrendered.

In 1803, weakened by malaria and yellow fever, a French invasion force led by Napolean's brother-in-law failed to suppress a native revolt on the French colony of Haiti.  This military fiasco, which resulted in Haiti's independence, probably discouraged Napoleon from establishing more footholds in the New World and may have even hastened his decision to sell the Louisiana Territory to the United States.

In 1814, Napoleon's military objectives were again thwarted by insect-borne disease when an outbreak of typhus stalled his troops as they attempted to invade Russia.  Over the course of a three-year campaign, 105,000 of Napolean's men were casualties of war and 219,000 were victims of insect-borne disease.

During the Crimean War (1853-55), an invading Russian army was overcome by hemorrhagic fever as it marched through the fly-infested swamps of southeastern Europe.  The allied forces of England, France, Turkey, and Sardinia easily defeated the weakened Russians and retained their military control over the region south of the Black Sea.

Yellow fever was a decisive factor in the Spanish-American War.  By the time the United States finally invaded Cuba in 1898, much of the Spanish occupation force was already debilitated by disease and unfit to fight.

Typhus (trench fever) plagued troops on both sides during World War I.  The disease was probably responsible for prolonging the war because neither side was healthy enough to wage a decisive battle.

Malaria played a major role in the fitness of armies on both sides of the American Civil War (1861-1865).  By the end of the war, 1.2 million cases had been treated and 8,000 soldiers had died.  Malaria was also a factor on the Macedonian front during World War I, in the Phillipines during World War II, and again in the Viet-Nam War where 80,000 cases were reported between 1965 and 1971.