The main ideology behind Germinal is forceful disagreement with the corruption of the aristocracy in France and the mistreatment of the lower classes in France during the Industrial Revolution.
In short, the ideology is exemplified the most by exploring the conditions that the workers are subject to in the mines of France during that time and specifically in the area of Montsou. The working conditions are just as deplorable as the living conditions there. The active mine there at the time is called the Voreux (and in French this means "voracious"). That is the truth, as this mine is literally voracious, swallowing up the workers in droves. The men who exit the mine (that is, those that don't die a horrible death because of it) are lacking all peace and all light that they may have had before their entrance to the mine.
In Germinal, unfortunately, the mood of the Voreux mine overshadows the entire town:
On a pitch black, starless night, a solitary man was trudging along the main road from Marchiennes to Montsou, ten kilometers of cobblestones running straight as a die across the bare plain between fields of beet.
Note how the images portray the ideology against the mining culture: a culture where a corrupt aristocracy feeds off the poor. Note how the night is "pitch black" just as the mine is pitch black. Note that the man is "trudging along" just as the poor workers trudge along in the mine.
In conclusion, and if we look deeper into the ideology, we will see that the Voreux mine is not the true problem. The real problem is the corrupt aristocracy. The board of directors is corrupt. It is this board of directors and all the aristocrats who squander the profits of the poor by living off the money made from the Voreux mine.