The Battle (war) of Chausa (June 26,1539) took place between Mughal Emperor Humayun and Sher Shah Suri (Sher Khan). Humayun was defeated in Chausa War by Sher Shah Suri.
Humayun divided his army into two parts and ordered Askari to take charge of the first division and proceed ahead. The second division under his personal command marched a few miles behind. At Munger the two divisions joined, and here, contrary to the advice of his seasoned officers, Humayun crossed the Ganga to its southern bank and took the old Grand Trunk Road towards Agra. This was a great mistake. Though Humayun now had the advantage of a better road, the southern route, which lay through South Bihar, was thoroughly under Sheer Shah’s control. The vigilant Afghan scouts regularly communicated to their master the movements of the Mughals army. It was the blunder on the part of Humayun which enabled Sher Shah to decide upon an open contest with him. The emperor, however, could not keep to the Grand Trunk Road and near Bihiya he was obliged to cross the Ganga back to its northern bank.
As Humayun reached Chausa, he received news that Sher Khan had reached the neighborhood. His officers were for an immediate attack on the Afghans who were tired as a result of several days’ journey, while the Mughal troops were, comparatively, fresh. But Humayun rejected their advice and decided to re-cross the river to its southern bank and wait there instead of attacking the enemy at once. The delay gave Sher Khan time to fortify his camp and to give the much needed rest to his men. A large number Afghan troop gathered under his banner. On the contrary, Humayun received little or no help from his brothers. Many of his troops deserted him on account of disease, hardship and fear of the enemy.
The armies of Sher Shah and Humayun lay facing each other for three months (April to June 26, 1539), but neither of them took up the offensive. Sher Shah purposely delayed the contest, as he felt that the coming of rainy season would hamper the Mughal army and give them a decided advantage over the. During the period there was an interchange of envoys for a peaceful settlement but it did not worked. The Afghan chief showed his hand as soon as the rains set in. the Mughal encampment, which stood on the low land between the Ganga in the north and the Karmanasa in the west, was flooded, causing confusion and indiscipline among its ranks.
Sher Shah made a surprise attack on the Mughals. The Afghan army, which was divided into three divisions under Sher Khan, his son Jalal Khan, ands his greatest general Khawas Khan respectively, attacked the Mughals from three directions. Consternation fell upon the imperialists. The whole of the Mughal army was was defeated. Humayun himself, attended by a few men, fled towards Agra.
In the battle fell eight thousand Mughals troops and a number of Mughal notables, including the restless Muhammad Zaman Mirza was eihter killed or drowned.