Mongols in India
October 2016 - Starting in the 400s AD, Turkic and Mongol people had been expanding out of the northern part of Central Asia and spreading all over Europe and Asia, first as the Huns, then the Avars, the Ghaznavids, the Seljuks. Abut 1000 AD, the Turkish Ghaznavids, based in what is now Afghanistan, invaded northern India. India was so rich that the Ghaznavids got a lot of plunder - gold and pearls - and they also took a lot of people and enslaved them. But by 1040, the Seljuks took power from the Ghaznavids, and the Seljuks took no interest in India and just left it alone.
A century and a half later, in 1192 AD, the Mamluks, who were also Turkic, invaded northern India and established the Delhi Sultanate, ruling northern India. Under the Delhi Sultanate, many people in northern India converted to Islam.
A video about the Mongols
By the early 1200s, the Mongols, under their king Genghis Khan, were conquering and uniting all of Asia - the Uighurs, the Kyrgyz, the Khitan - into one big empire stretching from Mongolia to Russia. In 1221 AD, the Turkic/Mongol expansion reached India for the first time as Genghis Khan sent his Mongol troops riding down from Iran and Afghanistan into India. By 1235, under Genghis Khan's son Ogedei and grandson Mongke, the Mongols ruled what is now Pakistan and Kashmir, in northern India. When Indian states got into wars, they started to ask the Mongol army for help, and soon the Mongols were soon the main power in all of northern India. But they didn't take over the Delhi Sultanate. They had enough problems with their empire already.
By about 1300, with the Mongols weaker and the Delhi Sultanate stronger under the new Khalji Dynasty, the Delhi Sultanate pushed the Mongols out of India with several big victories.
The Mongols invaded India once again in 1398, when an unrelated Mongol khan, Timur, was trying to rebuild the Mongol empire. Timur got as far as Delhi and sacked the city (he wrecked and plundered it). That ended the Delhi Sultanate, and left a power vacuum that was soon filled by yet another Mongol invasion - by a descendant of Timur's - which established the Mughal Empire.