It was however not simply annexed, but its area—now known as the "northern cities" (Mueang Nuea)—continued to be ruled by local aristocrats under Ayutthayan overlordship within the "mandala" model.

Phitsanulok, then the most important of the "northern cities", was subsequently ruled by Uparajas (viceroys), the designated heirs to the throne of Ayutthaya.

[3] Khun Phirenthorathep was one of the Sukhothai nobles brought to the court of Ayutthaya by Chairachathirat, who appointed him as head of the royal guard.

In 1548, the kingdom fell under the governance of Worawongsathirat and Chairachathirat's widow Si Sudachan of the Uthong dynasty.

Maha Thammaracha enjoyed a great power and may be referred to as a viceroy of the northern provinces.

However, the Siamese armies under Prince Ramesuan the Uparaja and Maha Thammarachathirat were ambushed and the two captured.

Maha Thammarachathirat offered "stout resistance", but surrendered and submitted after all food was gone and a smallpox epidemic spread.

In 1566, during Maha Thammarachathirat's absence from Phitsanulok to Pegu, Mahinthrathirat brought his sister Queen Wisutkasat and her sons and daughters to Ayutthaya.

In 1570, Barom Reachea III the King of Longvek marched his Cambodian armies to Ayutthaya and laid siege on the city but failed.

Naresuan sent Siamese armies to ambush the Cambodians at Chaibadan, halting the invaders from reaching Ayutthaya.