Access to oil was and still is a major factor in several military conflicts of the 20th century, including World War II, during which oil facilities were a major strategic asset and were extensively bombed. The German invasion of the Soviet Union included the goal to capture the Baku oilfields, as it would provide much-needed oil supplies for the German military which was suffering from blockades. 
Oil exploration in North America during the early 20th century later led to the U.S. becoming the leading producer by mid-century. As petroleum production in the U.S. peaked during the 1960s, the United States was surpassed by Saudi Arabia and the Soviet Union in total output.
In 1973, Saudi Arabia and other Arab nations imposed an oil embargo against the United States, United Kingdom, Japan and other Western nations which supported Israel in the Yom Kippur War of October 1973. The embargo caused an oil crisis. This was followed by the 1979 oil crisis, which was caused by a drop in oil production in the wake of the Iranian Revolution and caused oil prices to more than double.