Theory:

The Inception
  
The Delhi Sultanate spanned for 326 years and the Slave dynasty was the first dynasty of Delhi Sultanate. Muhammed Ghori founded the Muslim rule in India during the 12th century AD, and he developed a special set of slaves named "Bandagan”, as he doesn't have sons.
Bandagan - a Persian name used for slaves who were purchased for performing military services
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Slaves at work

Later on, these slaves were assigned the posting of governors and after some time they were raised to the status of sultans. Qutb-ud-din-Aibak, who was one among the slaves of Ghori claimed the territories of him post the death of Ghori in 1206 and self-proclaimed himself as the ruler of Turkish territories in India and thus he laid the foundation of the Slave dynasty in India. The slave dynasty spanned \(84\)years.
Mamluk dynasty: Slave dynasty is also known as Mamluk dynasty as Mamluk is an Arabic word meaning "Slave".
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Empire of Slave dynasty
Reign of Qutb-ud-din-Aibak : (1206 - 1210)
Qutb-ud-din-Aibak started his rule by keeping Lahore as his capital which he later changed to Delhi. He conquered new territories and at the same time kept rebellions in check. His military campaigns witnessed the conquest of the central and western part of Indo- Gangetic plain.
“Lakha Baksh”: Qutb-ud-din Aibak was highly generous so he was nicknamed Lakha Baksh Sultan
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Qutb -Minar

Meanwhile, Bhaktiar Khalji was left with the conquest of the eastern Gangetic plain (which comprised areas of Bihar, and Bengal).
 
Aibak built Quwwat-ul-Islam (Mosque) in Delhi and also laid the foundation stone for Qutub Minar which he was unable to complete, and later completed by Iltutmish (his son-in-law and successor). Aibak died in 1210 during a game of polo or chaugan and the injuries that he acquired accidentally at that time.
“ Chaugan/Polo”: A game which is played by sitting on a horse, Aibak died while playing this game
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Quwaat-ul-Islam Mosque
Quwwat-ul-Islam: Mosque which was built by Aibak in Delhi, considered to be the oldest in India.
Reign of Iltutmish: (1210 - 1236)
Iltutmish, the son-in-law of Aibak was chosen as the Sultan by the nobles as his son Aram shah displayed incompetence. Iltutmish who served as the commander of the Aibak later took resolute actions against rebels.
Tanka and Jital: Iltutmish issued Silver and Copper coins namely Tanka and Jital.
The Mongolian threat under Chengis Khan emerged during his period, he averted it tactically by denying shelter to Khwarezm Shah Jalal-ud-din who was chased out by Chengis Khan.
 
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Chengis Khan – The Mongolian King
 
Iltutmish organised "Chahalgani- a select group of 40 Turkish nobles " to counter the invasion of Mongols. Also known as "The Forty".
The "Iqta - land grants to the military officials instead of their regular wage" was granted by Iltutmish.
Iqtadars: The Iqta ( land ) holder is known as Iqtadars, who collected revenue from the Iqta assigned to them to maintain their horses and troops.
He also formed another group of people under the name of " Muqti - who are entitled to serve the sultan during the time of war ".
 
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Tomb of Iltutmish – Delhi

The Qutb-Minar was completed during his reign, of which the foundation was earlier laid by Aibak before his death.