Answer:
They began to centralize power.
Explanation:
For example, in medieval times, at the height of feudalism, kings did not have standing armies at their disposal, and had to tour the land, looking for military support from the nobles (feudal lords), whose armies were more loyal to them than to the monarch.
This changed as Europe entered the modern age. Kings began to rely on mercenaries and small professional armies, effectively reducing their dependency on military help from the feudal lords.
The same applies for taxation. Monarchs began to develop more efficient methods of tax collection that applied for the whole territory. In the modern era, the absolute kings of France like Louis XIV did not have to rely on the help of the nobles to collect taxes, they could collect all the taxes they needed on their own.
