skilled in stratergic warfare!!! The author here has matched the places listed in the Sabha parva description to a map of north India then followed poet's description as Bhima moves east wards.
(source: https://www.facebook.com/MahabharatKiGalatiyan )
Bhima's Eastern Campaign
When Bhima started on the Eastern Campaign, he was going up against the cream of Kshatriya aristocracy and power. In the east, the powerful kingdoms waited. According to later Greek writers Megasthenes and Arrian, 60% of Indian population was in Gangetic valley (Maa Ganga indeed) so these kingdoms were rich, populous and powerful. They included Panchala, Dasarna, Chedi, Kosala, Kasi, Malla, Mithila, Magadha, Anga, Pundra, Lauhitya and Vanga.
First Panchala was easy picking. Though there were Four kingdoms and Six tribes in these lands, the de jure King was Drupada. Even Bhima's son Sootasoma was an elected King of Somakas, one of the biggest tribes of Panchalas. Since days of Vishwaksena, the Panchala King who created the Samvidhana (constitution), Pancalas had preserved individual freedoms inside collective action. Vishwaksena is unique in Indian annals. There may have been earlier kings and maybe constitutions, Vishwaksena's s name is preserved thanks to his disciple Parasara and his disciple's son Ved Vyas. Panchalas would not be a problem, rather they would be an asset.
So, Bhima first went to Ahichhatra where Northern Panchalas ruled. (Bareilly district). Without fighting he persuaded them to join him. He then took Gandaki river kingdoms and Videha (Lumbini, Gandaki, Narayani, Janakpur zones of Nepal). Thus, securing the Siwalik Himalayan valleys, he can use the mountain fastnesses to descend on the Plains below.
Target Chedi
Bhima leaves his army in Siwaliks and with a small force moved suddenly and with speed and travelling through Panchala and Ekchakra, he surprised the Dasarna Kingdom (Bhilsa, Northern Madhya Pradesh). Sudharma came out with his army but Bhima challenged him to one on one combat. Sudharma agreed. Impressed by his valor, Bhima appointed Sudharma his commander-in-chief. His army is in north and now he has another, in one masterstroke Bhima doubled his army and won him loyal lieutenants. Sudharma would sacrifice his life pushing Bhima out of way of a sakti hurled by Bhagadatta in the Mahabharata War. (someone asked who could kill Pandavas, No one can with the friends they inspire and earn through their great deeds.)
Using Dasarna forces, Bhima took out the kingdoms on Vetravati including Karushas and then reached Narmada and defeated Pulindas. This way he also made the task of Sahadeva's southern expedition easier. By defeating Karushas and Pulindas, Bhima secured Sahadeva's rear and won him easy river crossings on Narmada.
Thus securing the southern section of his demesne, he moved towards Chedi (Bundelkhand) with army from South and Dasarna on West. He did not need to fight. Chedis were close cousins and Sisupala allied with Bhima's army and also gave him huge tribute. Resting there for 13 days, in a pincer movement, Bhima moved back north and took Kumardesh (Kannauj) across Ganga.
Target Kosala
Bhima had an army waiting in north in Siwaliks watching Northern Kosala and Gopalkaksha kingdoms. He had Chedis coming from south, he just secured Kannauj and thus surrounding Kosala on three sides. He attacked the premier Solar dynasty of Bharatavarsha. Brihadbala was defeated after struggle but Ayodhya king Dirghyagna was friendly and surrendered without fighting. With the resources of Awadh and Central UP under control, his northern army now moved and took out the kingdoms of Gopalkaksha (Gorakhpur) and Uttar Kosala (Sravasti, rest of Central UP) and using Siwaliks also annexed Malla (Central Bhojpur); moving towards mountains again, the middle Himalayas were also conquered including the eastern parts of Nepala, Upper Bihar, Sikkim and Darjeeling.
Target Kasi
Bhima's army was conquering Northern kingdoms in Himalayas while his army in central UP plains waited. Suddenly, leaving his army in North, Bhima appeared with his Chedi-Dasarna-Awadh forces against the Three Akshauhinis of Kashi King Subahu. Taken by surprise, Subahu was defeated and Kasi was now under Bhima. From there, his forces conquered Suparsva (Mirzapur), then suddenly, he leaves his plains army and moves fast back towards east to Darjeeling with his Northern army.
Target Mithila
Then the northern army dropped down from mountains onto the plains of North Bengal annexing and effectively encircling most of Bihar. He annexed North Bengal, Malda (Central Bengal) and Vardhaman (Burdwan), then swung his forces westwards into Jharkhand and took out Maddhara, Somadheya states (Jharkhand). He united his army at Kasi then turned North and took out Vatsa (Prayaga); then Bhargas (near Allahbad) then Nishadas and Manimana. Moving back, crisscrossing his own path across Jharkhand, he annexed Dakshin Malla, And Bhogvana (entire Jharkhand and Upper Orissa); then moving deep into Bengal, defeated Sarmakas and Varmakas (Bengal).
He now had annexed kingdoms to West, East and North of Mithila and he attacked Mithila. Mithila surprisingly fell very easily. Effective preparations have effective rewards. Resting there, he secured the entire north till Sikkim (Kiratas north of Indra Parvata). Then moving east he took out Central Bengali kingdoms.
Target Magadha and Anga
Look at the planning, Bhima moved out of Indraprastha, marching through Hastinapur territories, secured Panchalas as allies without fighting and then moved along Northern UP-Nepal border annexing all kingdoms till he touches Bihar border. Leaving an army detachment there, he returns through conquered territory and then moves through Panchala and Ekchakra to ally with Sudharma at Dasarna. Dasarana army then helps him conquesr most of MP and secure Narmada frontier. He then moves North and allies with Sisupala. First he uses Dasarna to remove Chedi allies in case that large and powerful kingdom decides to fight. Chedi does not. Using those allied armies he now defeats and annexes Central UP mainly Kosala and with pincer movements rest of UP is now secured. He rejoins the army he had left in North and allies with Mallas in North Bihar. He secures the mountains on his backs, and leaves an army at Darjeeling or Dinajpur. (Indra Parvata is Darjeeling)
He uses the Chedi forces from south and defeats next big enemy Kosala by encircling it. He rejoins the Chedi-Dasarna forces he had left in Kosala and becoming stronger with Ayodhaya forces. Bhima next annexes Kasi and Poorvanchal. Subahu and his three Akshauhinis fall; as Bhima uses his allies effectively and he had Kasi too encircled, an army in north, Chedis and Kosala on west and he coming in from South.
Bhima then moves back to join forces at Darjeeling, Moving south he is encircling Magadha and Anga both by taking out Bengal kingdoms. This army goes in complete circle from Darjeeling down to Burdwan and through Jharkhand completing the circle, he rejoins the Chedi-Dasarna-Kasi forces. With army reunited, he sends pincers to take care of Bhargas, Nishadas and cleared out all kings who are on borders of Magadha and Anga (Central Bihar). He then moves back east, clearing out and conquering whole of Jharkhand, (He had moved back and forth across Jharkhand twice, clearing out all kingdoms, thus totally isolating Magadha and Anga.) He then secures his back by taking out kingdoms deep in Bengal and easily defeats Mithila in north of Magadha.
So now, Bhima has armies to East, West, North and South of both Magadha and Anga. Then he moves in on Magadha and they do not fight. They had already made peace with the killer of Jarasandh. Their armies also joining in, Anga was attacked on all sides and Karna was thus defeated. Bhima prepared this assiduously. He gave due importance to the enemy (Know your self and know your enemy and in one hundred battles, you will never be in peril.), did not underestimate him and triumphed.
Bhima criss-crossed so many times, this is the heart of India. The Eastern campaign was through more than 60% of Indian population of the day. Many kingdoms and many rich states and strong armies. The confident general who leaves the army in Nepal and then runs down to Bhilsa in MP and challenges Sudharma to single combat! Then Sudharma and his army is used to conquer MP and then Chedi forces to annex Kosala and Kosala forces to annex Kasi while his northern forces swung around annexing Bengal and then through Jharkhand unite the armies and encircle the Bihar kingdoms of Mithila, Magadha and Anga. Meantime, Bhima criss-crosses again and again, encircling in case Magadha decides to fight and encircling Karna from all sides anyway. There was no chance for anyone to withstand him.
Again the akarmik kings of east and the Karmapradhana strategy of Bhima.
Poet describes his campaign and his sudden opening up of different fronts effectively. Bhima was energetic and mobile. He delegated and empowered his allies and officers. Thus, he found an army dedicated to him and willing to go to any lengths, through ravines of Vindhyas, forests of Jharkhand and high peaks of Siwaliks and Middle Himalayas.
Target Pundra and Vanga
After Anga, he easily defeats the Birbhum and Midnapore kings. Then he moves to next great challenge the Pundra King Vasudeva with his 2 Akshauhinis and defeats him. Already he had done the groundwork by securing kingdom and allies on all sides of Pundra. Then Vanga, Tamralipta and sea coast kings were easy pickings. Some of these kings may have been set up by Yudhishthara earlier when Kakshivana's sons were made kings in this region so Bhima probably had friendly faces among his opponents. He sends an army north to take Assam and Arunachal (Lauhitya) and a Navy south to take out island kings in Bay of Bengal.
Thus, he annexed entire East till the ocean.
Each major power was handled deftly. Each was encircled and then defeated.
To Quote Sun-Tzu, Bhima followed all his maxims:
His sudden moves and changing the front his army was engaged in.
Be extremely subtle, even to the point of formlessness. Be extremely mysterious, even to the point of soundlessness. Thereby you can be the director of the opponent's fate.
Picking and choosing his battlefields and time.
The good fighters of old first put themselves beyond the possibility of defeat, and then waited for an opportunity of defeating the enemy.
The quality of decision is like the well-timed swoop of a falcon which enables it to strike and destroy its victim.
The ever victorious march and its news running ahead and disheartening his enemies.
To fight and conquer in all our battles is not supreme excellence; supreme excellence consists in breaking the enemy's resistance without fighting.
Planning, Planning, Planning.
Victorious warriors win first and then go to war, while defeated warriors go to war first and then seek to win.
And the way, he ennobled, empowered and delegated responsibility to conquered kings:
Regard your soldiers as your children, and they will follow you into the deepest valleys; look on them as your own beloved sons, and they will stand by you even unto death.
Bhima was recommended to be the supreme commander-in-chief in Mahabharata war but his on-field abilities dictated that this role as warrior was more needed away from command responsibilities. His deputy in this campaign was certain Dhrishtadamyun.