More deaths have been attributed to war than have been caused by flea-carried plague.
Deaths caused by the plague
Bubonic plague has been confirmed to be the cause of the Plague of Justinian in AD 511-512 in the Eastern Roman Empire. (Wade, 2010) A high estimate is that this outbreak of the plague killed 25 million people. (Rosen, 2007)
During the Black Death, the plague is estimated to have killed 75 million (Dunham, 2008) to 200 million people (BBC News, 2001).
It killed 12.5 million during the Third Plague at the beginning of the 20th century. (Orent, 2004)
That gives a high-end estimate of 237.5 million deaths caused by the flea-caused Bubonic plague.
Deaths caused by wars
Wikipedia gives a list of wars by death toll. "These numbers usually include both the deaths of military personnel which are the direct results of battle or other military wartime actions, as well as the wartime/war-related deaths of civilians, which are the results of war induced epidemics, diseases, famines, atrocities, genocide etc."
- 60,669,200-84,589,300 – World War II (1939–1945)
- 30,000,000–60,000,000 – Mongol conquests (1206-1324)
- 27,000,000 – Second Sino-Japanese War (1937-1945)
- 25,000,000 – Qing dynasty conquest of Ming Dynasty (1616–1662)
- 20,000,000 – Taiping Rebellion (1850–1864)
- 16,563,868-30.000.000 – World War I/Great War (1914–1918)
- 16,000,000 – White Lotus Rebellion (1794-1804)
- 13,000,000 - An Lushan Rebellion (755–763)
- 10,000,000 – Era of Warring States (475 BCE–221 BCE)
- 10,000,000 - Red Eyebrows Rebellion (9-24)
- 8,000,000–12,000,000 – Dungan revolt (1862 –1877)
- 7,500,000 – Chinese Civil War (1927–1949)
These are only the top 12 of the estimated 3,023 wars (http://www.vency.com/wars.html) in recorded human history and the low-end estimate for the death toll across these wars is already 245 million.
BBC News. Decoding the Black-Death. October 3, 2001.
Dunham, William. Black death 'discriminated' between victims. ABC Science. January 29, 2008.
Orent, Wendy. Plague: The Mysterious Past and Terrifying Future of the World's Most Dangerous Disease. Simon and Schuster, 2004.
Rosen, William. Justinian's Flea: The First Great Plague and the End of the Roman Empire. Penguin, 2007.
Wade, Nicholas. Europe’s Plagues Came From China, Study Finds. New York Times. October 31, 2010.