Considering that he was not strong enough to engage in a fight with the sultan, Vlad was forced to pay tribute.
He used the time he thus gained to get rid of traitors and to organize; he fortified the city of Targoviste and built a stronghold at Poienari.
Knowing the unstable nature of the nobility he also made changes in the royal council surrounding himself with new people who had proven their loyalty.
Because during the coronation ceremony held at Arges the boyars were forced to take the oath of allegiance, he was able to command the immediate execution of the nobility who openly criticized him.

Those that were against him from the very beginning were impaled alongside their entire family, and others that were caught plotting against him were at first “spared” and then used for hard labor in the benefit of the ruler. All their assets being seized he had the funds to concentrate on building a personal army.
Is believed to attract all potential traitors trap used the following trick:

He invited to his house all small and large landowners in his country, when supper had ended he turned to the oldest and asked how many princes who ruled in that country he remembers. He answered how many he knew so Vlad turned to the others, young and old, and asked how many each recalls. One said fifty, some thirty, one twenty, another twelve, and none was so young to remember less than seven. He asked for all those lords to be impaled, and they were in number five hundred.

[translated from “Dracula” by Matei Cazacu, page 166]

The fragment is part of a German story, and the numbers are obviously exaggerated, but this scene was recognized even by the wallachian chronicle [revised and translated into Romanian in the 17th century], adding some details of psychological motivation and how landowners were sent to “work for the community”.
According to the chronicle, the feast took place at the royal court [remember the establishments he had in Chindia] on Easter. It is said that he invited not only the boyars but also all their family members. While the scene above described took place in the manor in between the council members and Vlad the Impaler, the family members were gathered and chained up. He impaled the old and took the young up at Poienari, where he made them work to death to raise the stronghold.
We are also given a reason for these seemingly cruel actions: upon investigating the death of his father and his older brother [remember that Vlad Dracul and his oldest son Mircea were killed by the boyars after they had tricked Hunyadi into believing Dracul would betray him] he found that his brother was turned in his grave – face down and twisted. He concluded that at least Mircea was buried alive and he took revenge on the people that killed his family.

๑۞๑ Related:๑۞๑
† Vlad the Impaler
† Count Dracula