"A vital interest is one on which a state will not compromise unless faced with irresistible military or economic pressure. Otherwise, it will resist to the very limit of its ability, including, if necessary, by war. A statesman who sets out to challenge another state’s vital interests must therefore be sure not only that his or her country possesses this overwhelming power, but that it is prepared actually to use it. Realists know that understanding what Russia and China will risk and why is critical to our policies going forward."