The first purely Indian troops employed by the British were watchmen employed in each of the Presidencies of the British East India Company to protect their trading stations. These were all placed in 1748 under one Commander-in-Chief, Major-General Stringer Lawrence who is regarded as the “Father of the Indian Army”

From the mid-eighteenth century, the East India Company began to maintain armies at each of its three main stations, or Presidencies of British India, at Calcutta (Bengal), Madras and Bombay. The Bengal Army, Madras Army, and Bombay Army were quite distinct, each with its own Regiments and cadre of European officers. All three armies contained European regiments in which both the officers and men were Europeans, as well as a larger number of ‘Native’ regiments, in which the officers were Europeans and the other ranks were Indians. They included Artillery, Cavalry and Infantry regiments, so historical sources refer to the Bengal/Madras/Bombay Artillery/Cavalry/Infantry (the latter often termed ‘Native Infantry’ or ‘N.I.’). From the mid-eighteenth century onwards, the Crown began to dispatch regiments of the regular British Army to India, to reinforce the Company’s armies. These troops are often referred to as ‘H.M.’s Regiments’ or ‘Royal regiments’.

In 1757, Robert Clive came up with the idea of sepoy battalions for the Bengal Presidency, which were to be armed, dressed and trained as the red coats and commanded by a nucleus of British officers. The Madras Army followed suit with six battalions in 1759 followed by the Bombay Army in 1767. Recruitment in all cases was done locally amongst single castes, from specific communities, villages and families.

In the Bengal Army however, recruitment was only amongst high caste Brahmin and Rajput communities, mainly of the Uttar Pradesh and Bihar regions. Recruitment was undertaken locally by battalions or regiments often from the same community, village and even family. The commanding officer of a battalion became a form of substitute for the village chief or gaon bura. He was the mai-baap or the “father and mother” of the sepoys making up the paltan (from “platoon”). There were many family and community ties amongst the troops and numerous instances where family members enlisted in the same battalion or regiment. The izzat (“honour”) of the unit was represented by the regimental colours; the new sepoy having to swear an oath in front of them on enlistment. These colours were stored in honour in the quarter guard and frequently paraded before the men. They formed a rallying point in battle. The oath of fealty by the sepoy was given to the East India Company and included a pledge of faithfulness to the salt that one has eaten

In Battle of Plassey the British force consisted of 613 Europeans, 171 artillery-men controlling eight field pieces and two howitzers, 91 topasses, 2100 sepoys (mainly dusadhs) and 150 sailors .

While Nawab’s army consisted of 30,000 infantry of all sorts, armed with matchlocks, swords, pikes and rockets and 20,000 cavalry, armed with swords or long spears, interspersed by 300 pieces of artillery, mostly 32, 24 and 18-pounders. The army also included a detachment of about 50 French artillerymen under de St. Frais directing their own field pieces. Siraj-ud-Daulah had a numerically superior force and made his stand at Plassey. The British, worried about being outnumbered, formed a conspiracy with Siraj-ud-Daulah’s demoted army chief Mir Jafar, along with others such as Yar Lutuf Khan, Jagat Seths (Mahtab Chand and Swarup Chand), Omichund and Rai Durlabh. Mir Jafar, Rai Durlabh and Yar Lutuf Khan thus assembled their troops near the battlefield but made no move to actually join the battle. Siraj-ud-Daulah’s army with 50,000 soldiers, 40 canons and 10 war elephants was defeated by 3,000 soldiers of Col. Robert Clive, owing to the flight of Siraj-ud-daulah from the battlefield and the inactivity of the conspirators. The battle was ended in 11 hours.

In Battle of Buxar British troops engaged in the fighting numbered 7,072 comprising 857 British, 5,297 Indian sepoys and 918 Indian cavalry. The combined army of the Mughals, Awadh and Mir Qasim consisting of 40,000 men was defeated by a British army .The Mughal camp was internally broken due to a quarrel between the Mughal Emperor Shah Alam II and Shuja-ud-Daula the Nawab of Awadh Mir Qasim was reluctant to engage the British, and instead went off to collect tribute. The lack of basic co-ordination among the three desperate allies was responsible for their decisive defeat.

Soon after the Battle of Buxar, Shah Alam II, a sovereign who had just been defeated by the British, sought their protection by signing the Treaty of Allahabad in the year 1765. Shah Alam II was forced to grant the Diwani (right to collect revenue) of Bengal (which included Bihar and Odisha) to the British East India Company in return for an annual tribute of 2.6 million rupees to be paid by the company from the collected revenue. Tax exempt status was also restored to the company. The company further secured for the districts of Kora and Allahabad which allowed the British East India Company to collect tax from more than 20 million people. East India company thus became the Imperial tax collector in the former Mughal province of Bengal (which included Bihar and Odisha). East India company appointed a deputy Nawab Muhammad Reza Khan to collect revenue on behalf of the company.

But the situation was different when they took on Hindus of Hindustan Mahadaji Shinde humbled the British in Central India, single handed, which resulted in the Treaty of Salbai in 1782, where he mediated between the Peshwa and the British. Only after death of Mahadaji they dared to expand further .

After the fall of Mysore in 1799–1800, the Marathas were the only major power left outside British control in India. The Maratha Empire at that time consisted of a confederacy of five major chiefs: the Peshwa (Prime Minister) at the capital city of Poona, the Gaekwad chief of Baroda, the Scindia chief of Gwalior, the Holkar chief of Indore, and the Bhonsale chief of Nagpur. The Maratha chiefs were engaged in internal quarrels among themselves. Wellesley had repeatedly offered a subsidiary treaty to the Peshwa and Scindia, but Nana Fadnavis refused strongly.

In October 1802, the combined armies of Peshwa Baji Rao II and Scindia were defeated by Yashwantrao Holkar, ruler of Indore, at the Battle of Poona. Baji Rao fled to British protection, and in December the same year concluded the Treaty of Bassein with the British East India Company, ceding territory for the maintenance of a subsidiary force and agreeing to treaty with no other power.

This act on the part of the Peshwa, their nominal overlord, horrified and disgusted the Maratha chieftains; in particular, the Scindia rulers of Gwalior and the Bhonsale rulers of Nagpur and Berar contested the agreement.

By that time British had 53,000 men to help accomplish their goals. In September 1803, Scindia forces lost to Lord Gerard Lake at Delhi and to Lord Arthur Wellesley at Assaye. Wellesley, who went on to defeat Napoleon at Waterloo, would later remark that Assaye was tougher than Waterloo.

On December 17, 1803, Raghoji II Bhonsale of Nagpur signed the Treaty of Deogaon in Odisha with the British after the Battle of Argaon and gave up the province of Cuttack (which included Mughalbandi/the coastal part of Odisha, Garjat/the princely states of Odisha, Balasore Port, parts of Midnapore district of West Bengal).

On 30 December 1803, the Daulat Scindia signed the Treaty of Surji-Anjangaon with the British after the Battle of Assaye and Battle of Laswari and ceded to the British Rohtak, Gurgaon, Ganges-Jumna Doab, the Delhi-Agra region, parts of Bundelkhand, Broach, some districts of Gujarat and the fort of Ahmmadnagar.

The British started hostilities against Yashwantrao Holkar on 6 April 1804. The Treaty of Rajghat, signed on 24 December 1805, forced Holkar to give up Tonk, Rampura, and Bundi.