Marxism is a worldview based on the theories of Karl Marx that sees capitalism as destructive because it creates an inevitable class struggle. More specifically, capitalism creates a war between the proletariat, or the working class, and the bourgeoisie, meaning the business-owning class or even upper middle class. Marxists see the proletariat as being oppressed by the bourgeoisie, which inevitably leads to war.
Emile Zola certainly portrays the Marxist worldview throughout his novel Germinal and, for the most part, presents the Marxist view favorably, showing it is a worldview worth agreeing with. Zola clearly portrays the bourgeoisie through the mining company, which is oppressing the proletariat, represented by the coal miners. More specifically, the mining company is oppressing its workers by lowering amounts paid to the workers due to the fact that coal prices have dropped as a result of overproduction. However, decreasing the amount paid to the workers puts them in even more desperate straights, leading to, just as Marx predicted, a strike. While Zola portrays the ensuing strike and the violence that accompanies it as inevitable, he also portrays Marxist extremism as dangerous. Souvarine is portrayed as a character who takes Marxist idealism to an extreme when he intentionally damages the mine as a means of damaging the mining company but also as a means of leaving his own mark on the world. Since Souvarine takes many lives through his actions, we can definitely see that Zola disagrees with his actions and the idea of allowing Marxist idealism to lead to such devastating violence.