Jarasandh conquered all lands barring Hastinapur(due to Bhishma and Karna) and Dwaraka (because of them hiding in forts near mountainous regions). All other kingdoms were either subservient to him, was his allies or their kings were captured for human sacrifice. Nothing comes close to matching his military power. Pandavs never induced a fraction of fear into enemies hearts as much as Jarasandha did..
And, O exalted one, the eighteen tribes of the Bhojas, from fear of Jarasandha, have all fled towards the west; so also have the Surasenas, the Bhadrakas, the Vodhas, the Salwas, the Patachchavas, the Susthalas, the Mukuttas, and the Kulindas, along with the Kuntis.
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. So also the Matsyas and the Sannyastapadas, overcome with fear, leaving their dominions in the north, have fled into the southern country. And so all the Panchalas, alarmed at the power of Jarasandha, have left their own kingdom and fled in all directions.
The sheer amount of terror he spread throughout indian subcontinent is visible from the above paragraph. Kingdoms fled at his mere NAME.
He married his daughters to one of Yadavs named kams and used him as a puppet to weaken the Yadavs from within.
Some time before, the foolish Kansa, having persecuted the Yadavas, married two of the daughters of Jarasandha. They are called Asti and Prapti and Are the sister of Sahadeva. Strengthened by such an alliance, the fool persecuting his relatives gained an ascendency over them all. But by this conduct he earned great obloquy. The wretch also began to oppress the old kings of the Bhoja tribe, but they, to protect themselves from the persecution of their relative, sought our help.
When Krishn and Balaram killed Kams, Jarasandha waged war against Yadavs(including krishn and balram). JS had 2 powerful generals Hams and dimvak who proved too much for Yadavs and were killed through trickery. Jarasandh' was depressed and withdrew from war. However kamsa’s daughter instigates him against Yadavs and he came back for war. Because the Yadavs had just tasted the might of Magadh army, it was obvious to them that they weren't even a match to it and devided to FLEE FOR THEIR LIVES. This included Krishn and Balarama too. Which simply shows how extraordinary of a threat he was.
Then, O bull of the Bharata race, king Jarasandha, hearing that both Hansa and Dimvaka had been killed, returned to his kingdom with an empty heart. After Jarasandha had returned, O slayer of all foes, we were filled with pleasure and continued to live at Mathura.
Then the widow of kansa and the daughter of Jarasandha, that handsome woman with eyes like lotus-petals, grieved at the death of her lord, went unto her father, and repeatedly urged, O Monarch, the king of Magadha, saying,--O slayer of all foes, kill thou the slayer of my husband.--
Then, O great king, remembering the conclusion to which we had come of old we became exceedingly cheerless and fled from Mathura. Dividing our large wealth into small portions so as to make each portion easily portable, we fled from fear of Jarasandha, with our cousins and relatives. Reflecting upon everything, we fled towards the west. There is a delightful town towards the west called Kusasthali, adorned by the mountains of Raivata. In that city, O monarch, we took up our abode. We rebuilt its fort and made it so strong that it has become impregnable even to the Gods.
Jarasandha forced the Yadavs to relocate from their homeland Mathura to Dwarka. Such was his reign of TERROR.
Krishn further says, defeating Jarasandh (at head of his army) is impossible and should be neutralised in a single combat where neither his army nor his allies would interfere. And that's exactly how he was eliminated.
He is incapable of being vanquished in battle even by all the celestials and the Asuras (fighting together). We think, however, that he should be vanquished in a personal struggle with bare arms. In me is policy, in Bhima is strength and in Arjuna is triumph; and therefore, as prelude to performing the Rajasuya, we will certainly achieve the destruction of the ruler of Magadha.
When we three approach that monarch in secret, and he will, without doubt, be engaged in an encounter with one of us. From fear of disgrace, from covetousness, and from pride of strength he will certainly summon Bhima to the encounter.
The man who has induced terror even to Krishn and forced them to abandon their homeland and flee for their lives, yet none of the serials or later adaptations depict it. Infact, Books focused on Krishn whitewashed this pathetic defeat of Krishn and turned Jarasandha many times weaker.
