The structure of society and warfare were closely connected to each other in the feudal system. The land belonged to the crown, the king assigned it to lords in return for military service, and in the case of war, the lords had to come with an agreed upon number of troops from their own estates.
However, this changed completely in the Renaissance and early modern period. The knights no longer ruled the fields. For example, the 30 years war was fought nearly exclusively by mercenary armies. As the war dragged along, the kings were out of money, and the mercenary armies sustained themselves by sacking or extorting cities. Late in the war, the opposing armies did not fight much with each other, they avoided another, maneuvered around for years, and many such armies lived off from what would be described today as a protection racket.
How can it be, that in this turbulent period of time, the ruling class remained stable, so that the "enlightened absolutist" monarchies what followed this time period were ruled mostly by the same families who were in power since the middle ages? I would have suspected, that the kings and the HR Emperor owned only a small number of own troops, and the biggest mercenary leaders could have risen to power. What stood in their way? Why couldn't have Tilly, for example, orchestrate a coup, similarly to what happened through modern times in South America or the Middle East?