Basarab supported Michael Shishman of Bulgaria's attack against the Kingdom of Serbia, but their united armies were defeated in the Battle of Velbazhd on the 28th of July 1330.

[13] On the same day, the pope sent similar letters to Charles I of Hungary and his high officials, including Thomas Szécsényi, the voivode of Transylvania, and Mikcs Ákos, the ban of Slavonia, asking them to support the Dominicans' actions against the "heretics".

[16] Historians Matei Cazacu and Dan Mureșan reject Djuvara's theory, saying that all other sources prove that Basarab was an Eastern Orthodox.

[24] One of those chronicles, Istoria Țării Românești, states that "Basarab" was the surname of an Oltenian boyar family, who accepted Radu Negru's suzerainty following his "dismounting".

[6][28] Basarab was first mentioned in a royal charter issued by Charles I of Hungary on 26 July 1324,[29] in which he was described as "our voivode of Wallachia".

[29][20] Historian István Vásáry states that Basarab only accepted Charles' suzerainty after the king restored royal authority in the Banate of Severin, a Hungarian border province, in 1321.

[30] In exchange for his loyalty, Basarab's possession of Severin Fort was confirmed, according to historians Tudor Sălăgean and Attila Bárány.

[13][31] A royal charter dated 18 June 1325 records that a person named Stephen, who was the son of a Cuman ispán in Hungary, stated that the king was weaker than Basarab and "did not even reach up to [his] ankle".

[11][10] A royal charter from 1329 listed Basarab, along with the Bulgarians, Serbs and Tatars, as an enemy who "[made] hostile inroads" around Mehadia.

[13][39] Taking advantage of the weakened state of Basarab's allies, Charles I of Hungary decided to restore his suzerainty in Wallachia.

[6][13] According to a royal charter issued two years after the events, Charles wanted to recapture "marginal lands" that Basarab "illegally" held in Wallachia.

[41][42] Charles continued his campaign, but he and his soldiers suffered from hunger while marching to Curtea de Argeș through a sparsely populated region.

[44] Archaeological research shows that after his capital of Curtea de Argeș was destroyed during Charles I's campaign, Basarab moved his seat to Câmpulung.

[46] The construction of the Princely Church of Saint Nicholas in Curtea de Argeș also commenced during Basarab's rule, but it was completed after his death.

[49] To prevent a campaign against Wallachia, Nicholas Alexander visited Louis I and swore loyalty to him, according to the nearly contemporaneous John of Küküllő's chronicle.

[52] Although the diptych (which was revised and renewed in 1710) may contain a scribal error, historians tend to accept that Basarab's wife was named Marghita (from Margarete).

"[6] Although the kings of Hungary continued to demand loyalty from the voivodes of Wallachia, Basarab and his successors yielded to them only temporarily in the 14th century.

[47] From the middle of the 14th century, Bulgarian, Hungarian, Moldavian and Serbian chronicles used the name "Basarab" when referring to Wallachia.