Seeing Bryan's previous recommendations, I am reading Paul Johnson's Modern Times for the first time. It is a bracing book, filled with opinions that differ from those of Progressive historians. On a number of minor points, I find Johnson less than persuasive. His veneration of Charles de Gaulle, for example.
Modern Times succeeds in making the case that Lenin, Stalin, Mao, and various third-world dictators deserve to be placed next to Hitler on the list of great villains of history. They shared a gangland method of retaining power by killing rivals and a social engineering strategy for which they were willing to commit mass murder.
As Bryan points out, Johnson wants to explain the emergence of these great villains as resulting from the growth of moral relativism. However, I think that Bryan is distorting Johnson's thesis by suggesting that the totalitarians "sold" their policies in terms of moral relativism. Instead, I think what Johnson means by indicting moral relativism is that this philosophy sapped the will of people to resist totalitarian leaders. Johnson seems to be saying that back in some halcyon day when people had religious faith and believed in objective morality, they would not have fallen for tyrants. His thesis is that as traditional religion faded in importance, it created a void that was filled by Communism, fascism, Nazism, and Third-worldism.
Some points that I would make:
1. Religion killed, too.
2. It is not clear that the 20th century was uniquely violent. Some (Steven Pinker, for example) would argue that humans have become less violent over time. The scale of violence reflects much larger population as well as technologies that kill more efficiently.
3. I do not think people need ethical relativism in order to rationalize not fighting tyrants. Fear can be quite sufficient.
In fact, I would argument that the main factor allowing the tyrant to emerge is a climate of fear, brought on by years of political violence. Hitler came to power in the middle of an era of vicious street-fighting between Communist and right-wing gangs. Lenin came to power in the middle of war that had already produced a revolution. Mao came to power after a long period in which China suffered from foreign invasion and domestic warlords.
Overall, I do not think that the "moral relativism" thesis can carry the weight that Johnson puts on it.
Having said that, I think that there is a larger point to be made, which is that people can rationalize violence in ways that, after the fact, seem horrifying. Johnson finds many instances of prominent individuals who praised Lenin, Stalin, Mao, and even Hitler.
I do not think that either moral relativism or moral absolutism are the answer. The moral relativist risks remaining neutral in situations where great evil is taking place. The moral absolutist risks making strong moral stands that ultimately rest on "My tribe is good, and the other tribe is bad."
I agree with Bryan that tribalism is bad. However, I also agree with Johnson to the extent that he is saying that we need to believe in moral absolutes that serve to restrain our use of violence to achieve our goals.