按照唯物辩证法的观点，自然界的变化，主要地是由于自然界内部矛盾的发展。社会的变化，主要地是由于社会内部矛盾的发展，即生产力和生产关系的矛盾，阶级之间的矛盾，新旧之间的矛盾，由于这些矛盾的发展，推动了社会的前进，推动了新旧社会的代谢。唯物辩证法是否排除外部的原因呢？并不排除。唯物辩证法认为外因是变化… - Mao Zedong

我这个人是被许多人恨的，特别是彭德怀同志，他是恨死了我的；不恨死了，也有若干恨。我跟彭德怀同志的政策是这样的：『人不犯我，我不犯人；人若犯我，我必犯人。』过去跟我兄弟也是这样。

Hence, if in any process there are a number of contradictions, one of them must be the principal contradiction playing the leading and decisive role, while the rest occupy a secondary and subordinate position. Therefore, in studying any complex process in which there are two or more contradictions, we must devote every effort to funding its principal contradiction. Once this principal contradiction is grasped, all problems can be readily solved. This is the method Marx taught us in his study of capitalist society. Likewise Lenin and Stalin taught us this method when they studied imperialism and the general crisis of capitalism and when they studied the Soviet economy. There are thousands of scholars and men of action who do not understand it, and the result is that, lost in a fog, they are unable to get to the heart of a problem and naturally cannot find a way to resolve its contradictions.

If the U.S. monopoly capitalist groups persist in pushing their policies of aggression and war, the day is bound to come when they will be hanged by the people of the whole world. The same fate awaits the accomplices of the United States.