This is an extract from the campaign on the Rhine of 1635, just to help people to see how was a military campaign in that era (extracted from the book Europe's Tragedy of Peter H. Wilson).
....Louis XIII was obligued to move his reserve army of 12.000 newly enlisted Swiss mercenaries to eject the duke from the west, while La Valette, La Force and Bernhard faced Gallas's invasion from the north. The two sides faced each otherin fortified camps near Moyenvic between 12 October and 23 November.
Both suffered terribly from the plague and malnutrition, just like Wallenstein and Arnim in 1633, or the two armies at Nuremberg the year before. The situation deteriorated more rapidly in the imperial camp where Duke Charle's arrival added to thepressure on resources, while Gallas spent days drinking. He finally gave up and retreated through Saverne in the snow, having been forced to leave his artillery behind because the soldiers had eaten the transport animals. His army lost up to 12.000 men, though french losses, including deserters, were probably at least as high....