Timur, the most treacherous Muslim raider and looter of Delhi 1397- 98

 Timur defeating Delhi Sultan,Mahmud Tughluq,Dec.1398 en.wikipedia.org

Timur bin Taraghay Barlas, commonly known in the West "Timur the lame," was a 14th-century warlord of Turco-Mongol descent. He conquered & ruled over much of western and central Asia, and founded the Timurid Empire and Timurid dynasty (1370–1405) in Central Asia, that survived until 1857 as the Mughal dynasty of India.

Timur, (reign-1370–1405) indianetzone.com

Timur, (reign-1370–1405) en.wikipedia.org

Timur was a great war commander, but equally he was  ruthless. He finally got into the foray in 1397 to amass wealth and invaded the Indian territory. He was only interested in India's vast wealth and not in expanding his kingdom.He was against idolatry and considered Christians and other faiths as infidels.'
 
 Timur started his expedition from Kabul in August 1398 and reached Delhi in December,1398. On his way to Delhi, he captured and looted all the towns. Sultan Mahmud Shah, the last Sultan of the Tughlaq dynasty and his Vazir’ (Prime Minister) fled from Delhi.

The Delhi Sultan's  army was already weakened by an internal struggle for succession to the throne within the royal family. Timur, being a strategist, was good at making the best out of a chaotic situation. As the Delhi army did not have a dynamic war leadership and lacked strategies to confront the mighty army of Timur, the Sultan's army was easily defeated on 17 December, 1398. Literally the disarrayed army was pulverized and blown to smithereens. Timur looted as much as he could, destroyed Delhi beyond redemption, and left vast areas  in ruin. 

Before the battle for Delhi, for about 15 days Timur went on a killing and plundering spree. mostly people of other faiths were ruthlessly killed.Timur himself recorded the invasions in his purported memoirs, collectively known as Tuzk-i-Timuri. Historian Irfan Habib writes:

...in  "Timur in the Political Tradition and Historiography of Mughal India" that in the 14th century, the word "Hindu" (people of 'Al-Hind', 'Hind' being "India") included "both Hindus and Muslims" in religious connotations.''Timur entered Delhi and the city was sacked, destroyed, and left in ruins. Before the battle for Delhi, Timur executed more than 100,000 "Hindu" captives.

The reason why Timur invaded India because he thought  there was too much religious tolerance being shown to the Hindus by the Muslim rulers  of Delhi. The aim of his invasion was to loot and  this situation. Before the worst rampage in  northern India, Timur had captured around 100,000 Hindu prisoners. Before confronting the ruler  Sultan Nasir-u Din Mahmud, Timur did not want to take chances with the Prisoners who might give full support to  the ruler.  He had all the prisoners -100,000 Hindus killed mercilessly. The order is detailed to an extent in Timur’s memoirs:'' I proclaimed throughout the camp that every man who had infidel prisoners should put them to death, and whoever neglected to do so should himself be executed and his property given to the informer. When this order became known to the ghazis of Islam, they drew their swords and put their prisoners to death. One hundred thousand infidels, impious idolaters, were on that day slain. Maulana Nasiruddin Umar, a counselor and man of learning, who, in all his life, had never killed a sparrow, now, in execution of my order, slew with his sword fifteen idolatrous Hindus, who were his captives.'' (https://listverse.com/2018/01/15/10-terrors-of-the-tyrant-tamerlane)

There were immense spoils of rubies, diamonds, pearls, gold and silver ornaments and vessels. According to Ruy Gonzáles de Clavijo, 90 captured elephants were specially employed merely to carry the booty consisting of precious stones, gold jewelry, etc looted from his conquest by Timur. 

Treasures were used to build mosques,etc at Samarkand. During his invasion in India (1398-99), capturing of slaves formed the main object for his army. 100,000 Hindu slaves had been seized by his soldiers and camp followers. Hindus under his rule had to pay the mandatory ''Jizya'' tax. Violation of Imperial ordinances by people, particularly of other faiths were severely dealt with and the punishments were harsh. 

His sudden invasion and mindless looting had a severe impact on the social life of people, including Muslims. They lost the food grains stored for their sustenance, standing crops, places of worships, beautiful buildings,monuments, wealth, homes,etc. Among the captured Hindu slaves, most of them were male skilled artisans, so there was a shortage of skilled workers in the work force. Another devastating effect on the vast Hindu population was the loss of male members creating a big gender gap. Child-marriage practice was introduced among the Hindus as an alternative to survive in a situation detrimental to the healthy growth of future generation. They thought, by marrying away their young female members at an early age, they could save  them and their lives from future  barbaric incidents.

This led to the disintegration of Delhi Sultanate and made the task easier  for the future invaders from NW of India.  

Ref:
 http://en.wikipedia.org/wiki/Timur

"Islamic world", in Encyclopædia Britannica, Online Edition, 2007. Quotation: "Timur (Tamerlane) was of Mongol descent and he aimed to restore Mongol power...."

Richard C. Martin, Encyclopedia of Islam and the Muslim World A-L, Macmillan Reference USA, 2004, ISBN 978-0-02-865604-5, p. 134.