The never-ending conflicts in the Middle East, mayhem in Libya, uncertainty in the Gulf and a war in Ukraine are all going to take a toll on the energy supplies this winter.
Russia sold 86 billion cubic meters of gas last year, all of which passed through Ukraine. Given what's happening there now, it is highly unlikely that the Russians would allow their gas to transit a country they are (unofficially) at war with. Just as it is unlikely that Ukrainians would allow Russian gas access through its territory.
Result? Many cold Europeans, many angry Europeans and many very pissed off Europeans. Many Europeans will have to make do without enough gas to heat homes, offices and factories. That's a bad prospect in northern European countries, where winter is no laughing matter. Winter defeated the armies of both Napoleon and Hitler.
And what does history tell us about cold, angry, pissed-off Europeans? Well, whenever two opposing camps got cold, angry and pissed off enough at each other in the past, they typically went to war.