" It is the political change in international relations as well as a change in superpower fortunes which indicate that the days of successful unilateral intervention are past and that multilateral military intervention might only succeed in exceptional circumstances. Even before the changes in these relationships had occurred, both the old USSR and the USA discovered in the most dramatic way the true impotence of their power in the intra-state conflicts of Afghanistan and Vietnam respectively. Not least, the cost of unilaterally inspired intervention was horrendous. The total bill for Vietnam was $190 billion while the Soviets spent $3-4 billion for each of the years their forces were fulfilling no useful purpose in Afghanistan.
The fact is that most military interventions undertaken this century should never have been embarked upon, for they were doomed for failure. The reason for this has tended to be due to misplaced faith in national capabilities as well as misappreciation of the size of the problem. By way of illustration it is appropriate first to relate international theory to the concept of military intervention, followed by a current overview essentially of the two states most traditionally involved in military intervention, the former USSR and USA. "
― , Military Intervention in the 1990s (The Operational Level of War)