This gloomy and eerie image is quite controversial in my opinion. Rain, in art, usually symbolizes abundance, jubilance, cleansing, and nourishment. Here it is used to create a dismal affect. The Bohemian protestants are going into Germany, raiding the land You can tell the war is not over yet because of the fire in the back. This painting may symbolize victory as it may have been painted by a protestant (it shows the Bohemians winning). But it also may be painted by a Catholic trying to represent the cruelty of the protestants. There are many casualties lying dead in the picture, clearly trying to attend to their daily errands. There is a man lying dead in front of his house who appears to have dropped food he was holding (most likely bread). Also, the roofs of the houses seem to be burnt down, so the protestants were not there only to kill the Catholics, but they were also there to destroy their village and take over their towns.
There are also two men bowing to the man in the front walking through on his horse clearly signifying that he is the war general, and also his army is a force not to be reckoned with.