Off course, it was preventable. Although the Japanese had their oil supply being choked, they had enough long to sustain its war of aggression in Southeast Asia, and they were turning to the Dutch East Indies, which had tons of oil reserves. However, they were deluded into thinking that such invasion would invite the U.S. Pacific Fleet, which had no plans on making a move to deter the Japanese there, serving as a reason for Japan's sneak attack on Pearl Harbor. The proximate cause for the oil embargo was that Japan occupied French Indochina, and had they withdrawn, the embargo would have ceased. But the Japanese felt that they could not back down and thus the war. The Japanese really made their choice in the early '30s when they started trying to conquer China, it's nobody's fault but the Japanese only and they learned it wisely after being nuked twice for its actions.