Marx's ideas also inspired the socialist movements and labor organizations that were instrumental in achieving vital reforms for workers. Millions of Europeans in industrialized countries joined leftist organizations whose leaders were influenced by Marxist thought. Most of the "brutal and murderous dictatorships" of the twentieth century seized on the strains of Marxism that they could use to provide ideological support for power. Others drew on other intellectual traditions. But North Korea has little to do with Marx as he was understood in his own time and immediately after, which was the topic of this question.
As for Einstein and Freud, both contributed to an atmosphere of intellectual uncertainty in the early twentieth century. Einstein seemed to suggest, among other things, that our understanding of the natural world was not based on knowable truths, and Freud argued that mankind was driven as much by irrational urges as by reason. Their work, along with thinkers like Nietszche, undermined many of the basic assumptions that educated Europeans had shared since at least the Enlightenment.
This mood was reflected in the art, music, and literature of the period, which tended to reject traditional conventions- think of writers like Kafka, painters like Picasso, and composers like Stravinsky. The First World War only accelerated this trend, giving rise to writers like Joyce and TS Eliot and artists like the Dada movement.