When Iltutmish ascended the throne in 1210 CE, his father-in-law's empire was split in 4 between Aibak's sons and Iltutmish retained the control of Delhi. He faced staunch opposition from the other sons and spent the next 10 years suppressing revolts and protecting his borders...Slowly and steadily, he got back many lost parts of the empire.
He also protected himself from the Rajputs. Iltutmish is remembered for his successful prevention of Mongol invasions. This began in 1221 when Changez Khan chased the ruler of Khwarzim to India. Iltutmish refused him asylum and Changez Khan stood at the banks of the Indus for 3 months before turning back. He strengthened his borders and the most elite soldiers were sent to the north-western borders. The successors of Changez Khan made numerous attempts to invade India but every attack was deflected by his armies. His actions consolidated the empire and set the foundations for the Sultanate which lasted for 300 years