The Hindustanis As the medieval period dawned, the northern regions of modern-day India were ruled primarily by the Gupta Empire. At its zenith under Chandragupta II Vikramaditya, this short-lived state stretched from the Indus River to the Ganges Delta. While exceptionally advanced for its time in economic, political, military, intellectual, and social terms, the Gupta Empire was overextended and vulnerable to external invasions. Nomadic incursions from the northwest posed a constant problem, as did the extremes of the local climates; flooding in particular was a major issue. This state would not outlive the 6th century AD, but it left a significant imprint on the polities that succeeded it. After the Gupta Empire fell, its possessions passed to the control of countless major and minor entities. These never matched the power of the Guptas, but they inherited its strengths and advancements: a sophisticated division of labor system, significant scientific achievements, bustling trade networks, and powerful military technology, to name a few. Sanskrit epics tell of a powerful and magnanimous 7th century ruler, Harsha Vardhana, who forged some of these polities into a pseudo-empire, but his state, too, had relatively little longevity. The next couple of centuries saw the emergence of a new threat as waves of Muslim invasions cascaded into the Indian subcontinent. While Indian magnates such as Bappa Rawal (8th century) initially succeeded in stemming the onrushing tide, this threat gradually grew too much for the often fragmented Indian states to muster sustained resistances. Beyond the Hindu Kush, powerful Turco-Persian Muslim dynasties were rising: the Ghaznavids had formed a formidable state in modern Afghanistan, Pakistan, and Iran. One particularly infamous ruler, Mahmud Ghaznavi (10th-11th century), launched seventeen separate campaigns to pillage much of North and West India. Following the Ghaznavids were the Ghorids, another powerful dynasty that toppled the Ghaznavids and thrust further into India during the 12th and 13th centuries. Both factions were notable for their heavy use of ghulams, former slaves who had been trained as professional soldiers, creating a warrior elite that dominated both battlefields and palaces. The Ghorid invasions were a watershed moment due to their permanent impact. Whereas their predecessors had merely led campaigns of pillaging and destruction, the Ghorids, under the brothers Ghiyath and Muhammad, defeated Prithviraj Chauhan of Ajmer and established permanent control over much of northern India. Their successor, Qutb al-Din Aibak, created a new superpower: the Delhi Sultanate (13th-16th centuries), which essentially consisted of a Muslim warrior-elite ruling over a culturally and socially majority Indian population. Like many of history's conquerors, the Delhi sultans deemed it infinitely more prudent to perpetuate the existing systems in their new empire than to attempt to tear them down and impose their own. The following centuries were tumultuous ones. The Delhi Sultanate and its neighbors were rattled by successive Mongol invasions which, while achieving no significant lasting gains, gutted the region's infrastructure. Particularly brutal was Timur/Tamerlane's invasion of 1398, which tore through northern India and reduced the glorious city of Delhi to a charnel house. Over a century later, the Mughal conqueror Babur - yet another Persified warlord from Central Asia - would remark in his autobiographical Baburnama that he observed a land not yet healed from the ravages of the past centuries. Nevertheless, Babur was able to mold the weakened northern Indian polities that he conquered into a powerful state, the Mughal Empire, which would rule the region from 1526 well into the early-modern period.