 Further, much of the oil consumed by affluent countries such as the United States is extracted in countries that are rather unstable politically, such as some of the members of the OPEC.The oil trade is therefore prone to become intertwined with international relations, although the nature of this interplay is highly controversial, with some citing oil as a reason for conflicts such as the Iraq War and others denying such claims.Finally, since the burning of fossil fuels releases carbon dioxide that was previously locked in the ground, humanity's reliance on oil may contribute to global warming.