What was the experience like for these soldiers and what were their own motivations for joining the British forces?

To answer this question we must first establish a few things. The Armies of the English East India Company were the precursor to the British Indian Army, which was itself the precursor to the Army of Independent India. The armies of the EEIC were divided into three Presidential Armies, these were the Bengal, Madras and Bombay Presidencies. These Presidencies themselves were the result of the establishment and expansion of "factories" (which were fortified settlements within which English traders stored their goods and used them as a selling station) by the EEIC between 1612 to 1757. These were established by acquisition of firmans which means edicts or grants from local rulers such as the Mughal Emperors, Mughal Governors or Marathas. By the middle of the 18th century, three factory towns, namely Madras, Bombay and Calcutta came into prominence as they grew in size and strength.

Eventually, the EEIC, began acquiring land and power in and around these fortified settlements, via a policy of supporting competing Indian princes in their wars for acquiring power. This was the experience of the Carnatic wars. The EEIC adopted a policy of helping native Nawabs and princes acquire power and promised to keep them secure while in return the Nawabs and princes gave them trade concessions. The EEIC also waged war against other companies and by 1757, had managed to kick out most of their competition. However, the watershed moment for the EEIC would come after their victory at the Battle of Plassey which assured them territorial rights in the Bengal province of the Mughal Empire. The conflict was the result of an Imperial Mughal firman being granted to the EEIC by then Mughal Emperor Farrukhsiyar, in 1717 giving the British East India Company the right to reside and trade in the Mughal Empire. They were allowed to trade freely, except for a yearly payment of 3,000 rupees. The company was given the right to issue dastak (passes) for the movement of goods, which was misused by company officials for personal gain. The transgressions of the company brought them into conflict with the Nawabs of Bengal, and the defeat of the Nawab at Plassey allowed the British to place their own candidate on the Throne, to acquire all the land within the Maratha Ditch and 600 yards (550 m) beyond it and the zamindari of all the land between Calcutta and the sea.

Now, we return to the Indian sepoy. The British had begun employing Indian sepoys to protect their "factories" as early as 1612 itself when the very first factories were established. However, initially these men served as watchmen and guards, with the passage of time, their function and proportion as part of the armed forces of the Presidencies grew significantly. By 1824, the size of the combined armies of Bengal, Madras, and Bombay was about 200,000 and had at least 170 sepoy and 16 European regiments. In 1844, the combined average strength of the three armies was 235,446 native and 14,584 European. For purposes of simplification, we shall take the example of the Bengal Presidency. The English shared the opinion that was common in India since the Ancient period, that there were certain "races" best suited for the purpose of war. These races had a "mercenary spirit, were of good stature and complexion, were drawn from the yeoman or land owning peasantry and were suitable for the style of warfare practiced in the Early Modern period". This led to these races being labelled as "martial races". Not surprisingly, these were the same "races" that had since the ancient and medieval period held the privilege to rule or to hold beaurocratic or military positions. Such as Brahmins, Rajputs, Muslims (Afghans, Iranians, Turks,), Khatris eventually Sikhs.

Hence, the sepoys of the Bengal Presidency, were in fact not recruited from the Provinces of Bengal or Bihar or Odissa. The British felt that the Bengalis were best suited for clerical work and that the South Indians were smaller in stature and lacked the physical robustness they wanted in their soldiers. Therefore, the entirety of the soldiers of the Bengal Presidency were drawn from the Kingdom of Oudh, which was an ally of the British ever since their Nawab was defeated by the Company at the Battle of Buxar and signed the Allahabad Treaty.

The soldiers that were recruited were mostly drawn from the Brahmin and Rajput castes of Oudh commonly known as Purbiyas. The term Purbiya originated in medieval India. It was used as a term to refer to mercenaries belonging to the Brahmin or Rajput caste from Oudh and Western Bihar. Throughout the medieval and early modern period, these were the preferred mercenaries highered, by mansabdars, Wazirs, Rajas and Mughal Emperors.

The process of recruitment was quite informal. For example, men who sought mercenary work were easy to find, usually the infantry of the native armies received little attention and soldiers could be convinced by promise of better prospects to join the army. In addition to this, the old feudal networks of recruitment were utilised as well, meaning "zamindars" (hereditary rulers of enormous tracts of land and the peasants who enjoyed land rights within their jurisdiction, from whom they reserved the right to collect tax on behalf of imperial courts or for military purposes) as well as serving officers and soldiers were required to encourage enlistment in the army among their estates, their family and close friends. To give you a perspective, by the early 19th century, this informal system of recruitment had become so well entrenched that the Brahmins of Oudh dominated the Bengal Presidential Army and represented 40% of it's total strength.

As far as their motivations are concerned, the common peasant of this period usually did not posses a sense of nationalism or nationhood. War was ever present and Nawabs/Rajas and dynasties were overthrown quite often. Usually men enlisted in the army either because they were Brahmins and Rajputs and belonged to a long line of soldiers and military adventures, hence tradition. Or because they were land owning Brahmins or Rajputs who required additional income and were looking for livelihood.

Now to discuss the experience that these soldiers went through. It should be no surprise, that despite being as able and as formidable as their European counterparts, the native soldier was paid less than his European counterpart, had very limited chances for promotion beyond the post of "subedar" or sergeant. Was required to take care of the manual duties of his European counterparts, such as carrying supplies, setting up tents etc. The campaigns were hard and the wars were constant. The Anglo Mysore wars of which there were 4, the Anglo-Maratha Wars of which there were 3, The first and Second Anglo-Sikh wars, the Anglo-Afghan wars and so on. The equipment of the native soldier was often comprised on. In any conflict, the death toll of the native soldier was always higher. Yet, there were a few bright spots for the soldier's life. Military service brought social recognition, the word of a subedar in the army, meant that his relative, for example his nephew who found himself facing a sentence at the local court could be spared on the promise that he would join the army. A steady flow of income was at least guaranteed and there was, until the early 19th century a feeling of camaraderie among the European officers and their native sepoys, since these officers felt that the well being of the sepoys was their responsibility.

But this wouldn't always be true and eventually, the older officer corps was replaced with a new batch of officers who saw India as the land of opportunity and plunder and cared less for their unit and native sepoys and more for acquisition of wealth to take back to England.