I think this question can best be answered with the help of an example. Here I'll provide an example of one of the biggest military failures in Indian military history, namely the Third Battle of Panipat, 14th of January, 1761.

THIRD BATTLE OF PANIPAT, 14TH OF JANUARY, 1761

BACKGROUND

It was during the reign of Akbar, and his successors that the Mughals saw a period of almost ceaseless expansion. Akbar had already conquered nearly all of North India as well as Afghanistan and Qandahar, and his successors, Jahangir, Shah Jahan and Aurangzeb, would take the Empire to even greater extents. Yet it was this practice of expansion, that would bring to the surface some of the most fundamental problems within the empire.

The Mughal Empire, like any other, was built upon its institutions. In this case, one such institution was the Mansabdari system. Under this system, each noble had a rank, consisting of zat and sawar, indicating his rank in court and his stipulated number of cavalry troops that he was required to maintain respectively. Usually, the payment of salaries to the nobility which was the de facto administration and military officer corps of the Empire was not done through cash but rather assigning land which would yield the required revenue owed to the noble. The system ofcourse had an obvious problem. The nobles being dependent on land to provide for their salaries and that of their soldiers, meant if the number of soldiers increased beyond an optimum level, there would be a mismatch between available land and number of nobles, this would put strain I the Imperial treasury and extend the Empire's resources to possibly untenable levels. This is what happened post 1707, when Aurangzeb breathed his last and shuffled off his mortal coil, leaving his empire unreformed, his institutions almost the same as they were under his father, his revenue and Mansabdari system under crisis and his nobility in factions, bent on intrigue.

It was this crisis, which exacerbated during the reign of Aurangzeb, mainly due to the fact, that there was very limited land to give anymore and the number of officers and soldiers was growing. Hence, officers became disloyal, soldiers became dissatisfied and the professional character of the army slackened. Not to mention the many diplomatic and internal conflicts that Aurangzeb was personally responsible for, which exacerbated and made the Mughal situation more desperate.

During his reign, in 1679, the kingdoms of Mewar and Marwar rebelled against him. This was a direct result of his ill-conceived attempt to include these kingdoms into Khalisa (lands directly administered by the Mughal Crown) lands by interfering in these state's matters of succession, a matter which was left upto the Rajputs by Akbar himself. While a peace treaty was signed with Mewar after a year, war with Marwar went on until after his death. Hence, by his own actions, he alienated the staunchest and most loyal allies that the Mughals had known and weakened the Empire irreparably.

Meanwhile, after the conclusion of the Mughal-Maratha wars that had waged for 27 years, the Marathas began a period of rise from the 1720's onwards. While the Mughal Empire experienced a period of incompetent leadership, of weak puppet Emperors controlled by powerful nobles from 1707-1720, the Marathas meanwhile went through they own internal strifes. Following Shivaji's death, a period of instability and constant all out war between 1680-1707, was ended when Aurangzeb died in 1707 and the son of Shivaji's eldest son Sambhaji, Shahu was released after having lived in Mughal captivity since 1689, following the Battle of Raigadh. After a brief civil war with his Aunt Tarabai, he seized the Maratha Throne. Early in his life, he appointed Balaji Vishwanath as his Peshwa. An office that had existed in the Sultanates of Deccan, and during Shivaji's reign was the highest office of the states financial concerns.

Yet, Balaji Vishwanath, not only served to bring the Maratha cause incredible fortunes, but through their exceptional diplomatic and military tact, he followed by his son Bajirao, and his grandson Balaji Bajirao expanded the Maratha territories from their initial kingdom's fringes to the north, with their influence reaching all the way to Attock by 1758. The reason for the success in the Peshwa Era, are largely credited to the efforts of Bajirao Ballal, the political tact of his son Balaji Bajirao and the successful Northern expeditions of his brother Raghunath Rao. Therefore, capitalising on the weakness of the Mughal Empire, the Marathas began expansion and after the reign of Bajirao, and during the reign of Balaji Bajirao the Peshwas had expanded Maratha territories and influence all the way to Attock.

Now we turn our attention to, Ahmad Abdali, who was born in the Sadozai clan of the Abdali tribe of Afghans in about 1722 CE. After having defeated the Russians and the Turks, Nadir Shah of Iran, had set out of Iran to punish the Afghans for their actions. During his invasions in 1732 CE, he captured two boys, brothers, Zulfiqar and Ahmad. Ahmad, distinguished himself in Nadir's service, quickly becoming a favourite and rose to the command of 3000 troopers in Nadir's personal guard. He was with Nadir Shah when Nadir invaded Delhi. When Nadir Shah was assassinated Abdali, took Nadir's seal, the Koh-i-Noor, valuables and a Mughal princess who was married to Nadir's son. He left for Afghanistan and took his troopers and many other Afghans with him, who elected him as their leader. And so, upon a Throne of dirt, with a crown of strewn grass, Ahmad Abdali, was made Ahmad Shah Abdali of Afghanistan. The Abdalis styled him Durrani Padshah or "Pearl Among Kings" and called themselves henceforth, Durranis.

He had claimed for himself, the provinces of the Mughal Empire that Nadir Shah had conquered which included Qandahar, Kabul, Peshwar, Lahore, Sindh, Ghazni, Hazara, Kohat, Bannu, Derajay, Qalat and Chahar Mahal. What followed was a series in brutal invasions by Abdali into the Mughal Empire, taking territory, slaves and leaving many razed cities and villages in their wake. These invasions were marked by a streak bigotry and persecution of Hindus in these regions. He conquered Sarhind in 1757 and thus acquired his claimed territories.

In 1758, Adina Beg Khan, Mughal Governor of Jalandhar Doab, allied with the Sikhs to push the Afghans out of Punjab. He soon realised that the Durrani would retaliate and take vengeance for this, and hence he approached the Marathas who were encamped at Delhi. Raghunath Rao accepted the offer and set out with a grand army. Raghunath Rao arrived to liberate Punjab and the west, he assaulted any and all Afghans between Delhi and Attock taking Peshwar, Multan, Sarhind, Punjab and Lahore. Finally, the stage was set, for the Third Battle of Panipat, since Abdali would invade to take back his territories, and the Marathas would be forced to offer a defense.