Since the time when humans first harnessed energy flows in nature, they have fought bitterly for control of those regions of the Earth that grant access to energy flows and storages. For most of human civilization, the most important sources of work were people and draft animals that were powered by renewable energy: the products of photosynthesis. Thus, the eternal struggle to capture the land of thy enemy was motivated in part by the increased ability feed horses and armies, which, in turn, provided greater means to capture other natural resources such as timber, water, and minerals.

The initial transition to inanimate forms of energy (wind and water) changed the object of the energy struggle but not its importance. Early industrial centers and trade relied on water for power and transportation. Water-powered factories and mills required precise locations on rivers, and the (free) mechanical energy of the flowing water of rivers provided a critical transportation link between resource-rich hinterlands and bustling urban centers of manufacture and trade. Control of rivers and watersheds thus became the focal points of military campaigns.

The Death of General Warren at the Battle of Bunker Hill, by John Trumbull.: Note the image of the white pine in the colonists' flag, symbolic of its strategic importance. The sailing ship was an especially transformative energy conversion system. Prior to the sailing ship, ocean transport required vessels powered by human labor, an inefficient mode due to the low power output of the human body and the space and weight occupied by the food and space required to fuel the laborers. The energy source for the sailing ship was free, and, under the right conditions, very powerful. Masts become a vital necessity to nations. When the Dutch cut-off English access to the forests of the Baltic countries in 1654, England turned to the colonies in America to harvest it great forests of white pine. The old English sign of naval property, the "Broad Arrow," appeared on all trees over twenty-four inches in diameter by 1691. Tensions over timber supply escalated as colonists' domestic need for timber grew, and were a major factor leading to the outreak of the Revolutionary War.

Baku oil fields, 1918. Source: BBC Conflict over energy reached new heights in the oil era because the economic and geopolitical stakes were much higher. World War I was the first global conflict in which energy played a central role. The war machine was a combination of traditional technology (people and horses) with oil-based mechanization (planes and tanks). Both the Entente and Central powers knew that control of oil was a key to victory, and they wanted access to key oil regions when the political boundaries were redrawn by the victors. Case in point is the Caspian Sea basin, and especially Baku, the birthplace of the international oil industry. A various points in the war, Armenians and British forces defended Baku oil fields for Russia against German and Turkish invaders. In 1920, when the Bolsheviks captured Azerbaijan, all private property- including oil wells and factories - was confiscated. The Republic's entire oil industry was subsequently directed toward the purposes of the Soviet Union, including a tremendous output of oil for the World War II effort.

Oil was central to the strategy and execution of World War II. In response to Japan's invasion of China, the U.S. cut off oil exports to Japan in July 1941. Without domestic sources and thus starved for oil, Japan invaded the oil rich Indonesian islands. These tensions were a direct contributor to the attack on Pearl Harbor and the U.S entry into the war.

Hitler declared war on the Soviet Union in 1941 in part to secure oil for his war machine. He launched Operation Blau, a campaign designed to protect Nazi oilfields in Romania while securing new ones in the Caucasus. To do this he needed control of Stalingrad (now Volgograd). The ensuing Battle of Stalingrad, conducted between between August 21, 1942 and February 2, 1943, is viewed as one of the turning points of the war in the European Theater, and is among the bloodiest battles in human history, with combined casualties estimated to be above 1.5 million.

U.S. war planes over the oil fields of Kuwait, 1991. The Gulf War or Persian Gulf War (August 1990 to February 1991) centered on the control of oil and the power that flows from that control. Iraq's invasion of Kuwait gave it control of more than 220 billion barrels of oil, an amount that rivaled the reserves of Saudi Arabia, the worlds largest holder of reserves. This would have given Iraq significant influence in the world oil market, a position that the U.S. and other oil consuming nations views as untenable. The U.S. led invasion centered around the return Kuwait to the control of the Emir of Kuwait and with it control of that nation's oil holdings.

Sources

• Arima, Yuichi, The Way to Pearl Harbor: US vs Japan, Inventory of Conflict and Environment, American Univesity, Accessed 15 March 2008.
• Cottrell, W. Fred, Energy and Society, McGraw-Hill, NY, 1955.
• Grau, Lester W., Hydrocarbons and a New Strategic Region: The Caspian Sea and Central Asia, Military Review, May-June 2001.
• Yergin, Daniel. The Prize: The Epic Quest for Oil, Money & Power. Simon & Schuster, 1991.