In September 1330, Charles launched a military expedition against Basarab I of Wallachia who had attempted to get rid of his suzerainty.
After seizing the fortress of Severin (present-day Drobeta-Turnu Severin in Romania), he refused to make peace with Basarab and marched towards Curtea de Argeș, which was Basarab's seat.
The Wallachians applied scorched earth tactics, compelling Charles to make a truce with Basarab and withdraw his troops from Wallachia.
While the royal troops were marching through a narrow pass across the Southern Carpathians on 9 November, the Wallachians ambushed them.
During the next four days, the royal army was decimated; Charles could only escape from the battlefield after changing his clothes with one of his knights, Desiderius Héder, who sacrificed his life to enable the king's escape.
Charles did not attempt a new invasion of Wallachia, which subsequently developed into an independent principality.

In September 1331, Charles made an alliance with Otto the Merry, Duke of Austria, against Bohemia.
He also sent reinforcements to Poland to fight against the Teutonic Knights and the Bohemians.
In 1332 he signed a peace treaty with John of Bohemia and mediated a truce between Bohemia and Poland.
In 1332 Charles allowed the collection of the papal tithe (the tenth part of the Church revenues) in his realms only after the Holy See agreed to give one third of the money collected to him.
After years of negotiations, Charles visited his uncle, Robert, in Naples in July 1333.
Two months later, Charles's son, Andrew, was betrothed to Robert's granddaughter, Joanna, who had been made her grandfather's heir.
Charles returned to Hungary in early 1334.
In retaliation for a previous Serbian raid, he invaded Serbia and captured the fortress of Galambóc (now Golubac in Serbia).

In summer 1335, the delegates of John of Bohemia and the new King of Poland, Casimir III, entered into negotiations in Trencsén to put an end to the conflicts between the two countries.
With Charles's mediation, a compromise was reached on 24 August: John of Bohemia renounced his claim to Poland and Casimir of Poland acknowledged John of Bohemia's suzerainty in Silesia.
On 3 September, Charles signed an alliance with John of Bohemia in Visegrád, which was primarily formed against the Dukes of Austria.
Upon Charles's invitation, John of Bohemia and Casimir of Poland met in Visegrád in November.
During the Congress of Visegrád, the two rulers confirmed the compromise that their delegates had worked out in Trencsén.
Casimir III also promised to pay 400,000 groschen to John of Bohemia, but a part of this indemnification (120,000 groschen) was finally paid off by Charles instead of his brother-in-law.
The three rulers agreed upon a mutual defence union against the Habsburgs, and a new commercial route was set up to enable merchants travelling between Hungary and the Holy Roman Empire to bypass Vienna.

The Babonići and the Kőszegis made an alliance with the Dukes of Austria in January 1336.
John of Bohemia, who claimed Carinthia from the Habsburgs, invaded Austria in February.
Casimir III of Poland came to Austria to assist him in late June.
Charles soon joined them at Marchegg.
The dukes sought reconciliation and signed a peace treaty with John of Bohemia in July.
Charles signed a truce with them on 13 December, and launched a new expedition against Austria early the next year.
He forced the Babonići and the Kőszegis to yield, and the latter were also compelled to hand over to him their fortresses along the frontier in exchange for faraway castles.
Charles's peace treaty with Albert and Otto of Austria, which was signed on 11 September 1337, forbade both the dukes and Charles to give shelter to the other party's rebellious subjects.

Charles continued the reform of coinage in the late 1330s.
In 1336, he abolished the compulsory exchange of old coins for newly issued coins for villagers, but introduced a new tax, the chamber's profit, to compensate the loss of royal revenues.
Two years later, Charles ordered the minting of a new silver penny and
In September 1330, Charles launched a military expedition against Basarab I of Wallachia who had attempted to get rid of his suzerainty. After seizing the fortress of Severin (present-day Drobeta-Turnu Severin in Romania), he refused to make peace with Basarab and marched towards Curtea de Argeș, which was Basarab's seat. The Wallachians applied scorched earth tactics, compelling Charles to make a truce with Basarab and withdraw his troops from Wallachia. While the royal troops were marching through a narrow pass across the Southern Carpathians on 9 November, the Wallachians ambushed them. During the next four days, the royal army was decimated; Charles could only escape from the battlefield after changing his clothes with one of his knights, Desiderius Héder, who sacrificed his life to enable the king's escape. Charles did not attempt a new invasion of Wallachia, which subsequently developed into an independent principality.
In September 1331, Charles made an alliance with Otto the Merry, Duke of Austria, against Bohemia. He also sent reinforcements to Poland to fight against the Teutonic Knights and the Bohemians. In 1332 he signed a peace treaty with John of Bohemia and mediated a truce between Bohemia and Poland. In 1332 Charles allowed the collection of the papal tithe (the tenth part of the Church revenues) in his realms only after the Holy See agreed to give one third of the money collected to him. After years of negotiations, Charles visited his uncle, Robert, in Naples in July 1333. Two months later, Charles's son, Andrew, was betrothed to Robert's granddaughter, Joanna, who had been made her grandfather's heir. Charles returned to Hungary in early 1334. In retaliation for a previous Serbian raid, he invaded Serbia and captured the fortress of Galambóc (now Golubac in Serbia).
In summer 1335, the delegates of John of Bohemia and the new King of Poland, Casimir III, entered into negotiations in Trencsén to put an end to the conflicts between the two countries. With Charles's mediation, a compromise was reached on 24 August: John of Bohemia renounced his claim to Poland and Casimir of Poland acknowledged John of Bohemia's suzerainty in Silesia. On 3 September, Charles signed an alliance with John of Bohemia in Visegrád, which was primarily formed against the Dukes of Austria. Upon Charles's invitation, John of Bohemia and Casimir of Poland met in Visegrád in November. During the Congress of Visegrád, the two rulers confirmed the compromise that their delegates had worked out in Trencsén. Casimir III also promised to pay 400,000 groschen to John of Bohemia, but a part of this indemnification (120,000 groschen) was finally paid off by Charles instead of his brother-in-law. The three rulers agreed upon a mutual defence union against the Habsburgs, and a new commercial route was set up to enable merchants travelling between Hungary and the Holy Roman Empire to bypass Vienna.
The Babonići and the Kőszegis made an alliance with the Dukes of Austria in January 1336. John of Bohemia, who claimed Carinthia from the Habsburgs, invaded Austria in February. Casimir III of Poland came to Austria to assist him in late June. Charles soon joined them at Marchegg. The dukes sought reconciliation and signed a peace treaty with John of Bohemia in July. Charles signed a truce with them on 13 December, and launched a new expedition against Austria early the next year. He forced the Babonići and the Kőszegis to yield, and the latter were also compelled to hand over to him their fortresses along the frontier in exchange for faraway castles. Charles's peace treaty with Albert and Otto of Austria, which was signed on 11 September 1337, forbade both the dukes and Charles to give shelter to the other party's rebellious subjects.
Charles continued the reform of coinage in the late 1330s. In 1336, he abolished the compulsory exchange of old coins for newly issued coins for villagers, but introduced a new tax, the chamber's profit, to compensate the loss of royal revenues. Two years later, Charles ordered the minting of a new silver penny and 
Charles I of Hungary