The correct answer to this open question is the following.
What brought the power of Delhi to an end was basically conflicts and invasions of its enemies. For instance, the Turkish invasion of warrior Timur in 1398, that invaded Delhi territory with the troops of Turkey. By 1414, the Delhi Sultanate power was severely limited to a country power that competed with other Hindu and Muslim authorities. But the sultanate could not resist followed Mongol invasions that brought the power of Delhi to an end.