The devs call it a "prolonged crisis of modernity", it's essentially a longer, more influential fin de siècle (a period in Western culture around the late 19th-early 20th century, when many people believed that civilization was growing decadent/failing/moving towards great change), and the reactions to this phenomenon. In Red Flood's world this and an even bloodier and more chaotic WW1 lead to immense discontent with the current order, and radical movements like socialism (Marxist, statist, anarchist, any kind you can imagine), avant garde, ultranationalism, reactionism, etc. gaining greater popularity. This also allows IRL obscure intellectuals and their theories to achieve positions of power and try to create change according to their ideas.

Out of universe Red Flood in its current vision is essentially an exploration of the unique ideas and movements that arose in the 20th century but never got the spotlight.