Pope Pius the 2nd agreed with the observations of Vlad the Impaler, so he sent large sums of money to Matthias Corvinus for him to better equip the military and rush to the aid of Wallachia.
As Vlad predicted, Mehmed went against him with an army of about 200,000 people – estimated numbers are of at least 150,000 up to 250,000 maximum so I chose the middle because the documents considered by historians to be reliable, but not agree to this single matter. Vlad only gathered 25,000 to 30,000 maximum to oppose the crunching force gathered to trmple Wallachia; it was the second army [in size] after the one used in the siege of Constantinople.
Matthias promised to join the fight, but he never did. Even more so he used the financial aid sent by the Pope to support his dream of redeeming the Habsburg crown to Frederick [according to documents presented at the History Museum of Vienna, Matthias paid for the crown around 80,000 gold ducats – an enormous amount].
When the sultan reached the Danube River with the intention of passing on the Romanian territory at Turnu [Magurele], no one expected Vlad the Impaler to have any chance against the Conqueror of Constantinople; in addition to the numerical advantage, the sultan’s troops were much better equipped and trained.
The Romanian army was composed of peasants gathered from the field, who had to bring their own armor.
Moreover, Vlad was betrayed by his cousin, Stephen the Great!
While the Turks attacked the city of Chilia on water, Stefan sieged from land. Thus Vlad was forced to divide the army and send 7000-8000 horsemen in garrison of the much needed port.
Chilia was lost to the traitor and Mehmed`s army managed to cross the Danube.
What followed was recorded in all the chronicles and impressed all contemporary strategists as well as the future royal courts. Although no one believed that Vlad could come out victorious, he managed to win the psychological war long before arms were crossed.
The sultan was so horrified by the Forest of the Impaled near Targoviste, that he withdrew from Walachia and Chalkokondyles wrote in his chronicle:

“Even the king, filled with wonder, said he could not meet a man who makes things so great and beyond nature, knowing to use both his country and his subjects.”

He also said that the man who is capable of so much would deserve more. ”
So, besides the fear that had seized the whole army, the sultan felt respect and admiration for Vlad. Probably the Conqueror of Constantinople recognized in the Wallachian prince a worthy adversary!
It is hard to imagine how things would have been if Vlad was supported and not cornered from all sides.
But what facts could have been so grotesque as to frighten the Sultan?
Vlad’s strategy had several key points:
§ instead on engaging in a battle plain, the Impaler chose to “retreat” to Targoviste, being careful to harass his opponent all the way.
§ he took the time and emptied all settlements along the road followed by the Turkish army, offering shelter for the population and animals in the surrounding forests

When they learned that the king comes upon them, they took the women and infants in a safe place, some in the mountains [Carpathians], others in a small city … [empty space, maybe Bucharest] surrounded by marshes; the were guarded and fully sheltered. Others have moved in the woods that are hard to pass if someone comes from elsewhere and is not of that place.
[…]
Therefore, they protected the women and children. As for them, they gathered in one place, and then they followed their master Vlad the Impaler.

[Extract from the Chronicle of Chalkokondyles, translated from “Dracula” by Matei Cazacu, page 200]

§ all the fields and crops were burned, and the wells were hidden, so that the Turks were always hungry and thirsty, and their horses were dying of dehydration.
There are mentions that there would be poisoned wells, but is unlikely because there would have been used by locals after the withdrawal of the Turks so it`s more likely that they simply hid them of made them in some way inaccessible.
§ there were no confrontations between armies because Vlad was aware of the numerical advantage of the sultan, so he preferred to remain hidden in the woods. Thus he avoided significant losses, and the Turks lost not only in strength but also moral.
§ when the sultan sent a contingent in search of food [in settlements that were not so close to the road they used], they did not return as if they were simply “swallowed” by the woods of Wallachia.
§ raids were taking place almost every night, during which the extremities of the Turkish camp were attacked and the enemies continually felt threatened.
One of these raids was so terrible that it remained recorded in several reviews.
It’s the attack on the night of 17 to 18 June, when Vlad was very close to fulfilling his desire to kill the sultan.
When they arrived near Targoviste and saw the Forest of the Impaled, the Turks were already drastically demoralized, exhausted, sick, frightened almost to madness.

The Hungarian army was supposed to come in support of Vlad, or so the sultan believed… so he left Wallachia, but ordered Vlad`s younger brother to camp on the Bulgarian border.
His oratorical skills were renowned and Mehmed`s hopes were not in vain because the landowners left Vlad`s side one by one.
Radu was put on the throne of Targoviste while Vlad was in Brasov with Matthias; the latter recognized his reign of Radu the Handsome and took the Impaler with him … as a prisoner in Hungary!

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