Rama's brother Bharata, colonized the Gandhara kingdom and founded the city of Takshasila and his descendants named as Gaud kshatriya.

Rama's second brother Lakshmana founded the city of Lakshmanapura near river Ganges which is now known as Lucknow and his descendants named as Pratihara.

Rama's youngest brother Satrughna destroyed the forest of a demon named Madhu and founded the city of Mathura which later became the capital of the Surasena Kingdom.

Brihadbala another ruler of Kosala during Dvapara Yuga, took part in Mahabharata war and was killed by Abhimanyu, the son of Arjuna.

Raghava Rama's son's Lava and Kusa, inherited each half of the Kosala kingdom, with Ayodhya as its capital.

During the time of Kurukshetra War, and the reign of Pandavas and Kauravas, we find mention of numerous kingdoms with the name, Kosala (as per the references in Mahabharata).

This became evident if we follow the passage in Mahabharata, describing the military campaign of the Pandava general Sahadeva, who led his troops to the southern direction.

And the king of the Salwayana tribe with their brethren and followers; and the southern Panchalas and the eastern Kosalas have all fled to the country of the Kuntis.

Passing over the hills of Kalakuta, they then went on crossing the Gandaki, the Sadanira (Karatoya), and the Sarkaravarta and the other rivers taking their rise in the same mountains.

Then the foremost of the sons of Pandu, by performing feats excelling in fierceness, defeated the virtuous and mighty king Dirghayaghna of Ayodhya.

This is that mighty mountain called Vindhya; yon, the river Payasvini running seawards, and yonder are the asylums of the ascetics, furnished with various fruit and roots.

What is the occasion of this thy visit?’ And king Bhima asked this without knowing that Rituparna had come to obtain the hand of his daughter.

Sojourning next to the tirtha called Rishabha in Kosala and fasting there for three nights one earneth the merit of the Vajapeya sacrifice, and of the gift of a thousand kine, and also delivereth his race.

And having taken Batsa-bhumi, he reduced Kevali, and Mrittikavati, and Mohana and Patrana, and Tripura, and Kosala,--and compelled all these to pay tribute.

The loss of thy kingdom, and then the death of our father, and then the abduction of Sita, and finally this disaster that hath overwhelmed me!

Alas, I shall not behold thee return with the princess of Videha to Kosala and seated on thy ancestral throne as the ruler of the entire Earth!

That descendant of Raghu, who ruleth at Kosala and whose renown hath spread over the whole world, sayeth unto thee these words suited to the occasion.

King Vrihadvala of Kosala, supported Duryodhana in the Kurukshetra War Then came Kritavarman at the head of his troops, and that mighty car-warrior, viz., the ruler of the Trigartas, and the king Duryodhana surrounded by his brothers, and Sala, and Bhurisravas, and Salya, and Vrihadratha, the ruler of the Kosalas.

These and many other kings and princes, mighty car-warriors conversant with policy, obedient to the commands of Duryodhana, all cased in mail, were seen stationed in their respective divisions.

The son of Subhadra then upon the overthrow of his charioteer, was filled with wrath and pierced Vrihadvala The ruler of the Kosala struck Abhimanyu, in the chest with a barbed arrow.

The ruler of the Kosalas, then, thus deprived of his car, took up a sword and wished to sever from Abhimanyu's trunk his beautiful head, decked with ear-rings.

The sacrificial horse then, equipped with beautiful manes, proceeded at his will along the sea-coast, repairing to the countries of the Bangas, the Pundras, and the Kosalas.

It hath been heard by us that once on a time the sage Kalakavrikshiya came to Kshemadarsin who had ascended the throne of the kingdom of Kosala.

Saudasa, the king of Kosala, though dignified by the performance of Ashwamedha and other sacrifices, obtained the status of a man-eating Rakshasa, through the curse of a great Rishi.