Which Sultan of the Delhi Sultanate is often credited with completing the conquest of large parts of the south and breaking the political barrier between northern and southern India?

Introduction / Context:
This question focuses on the territorial expansion of the Delhi Sultanate into the Deccan and South India. Several rulers launched campaigns towards the south, but one Sultan in particular is often described as having broken the political barriers between the north and the south by extending his authority over a very large area.

Given Data / Assumptions:

The question refers to the Delhi Sultanate period, not the Mughals.
We need the ruler associated with extensive southern campaigns and integration attempts.

Concept / Approach:
Although Alauddin Khalji initiated major Deccan campaigns through his general Malik Kafur, Muhammad bin Tughluq expanded the empire even further, attempting to rule almost the entire subcontinent. His decision to shift the capital to Daulatabad shows his ambition to integrate northern and southern regions under one central authority, which is why many accounts credit him with breaking the political barrier between the two.

Step-by-Step Solution:
Recall that Alauddin Khalji sent expeditions into the Deccan but did not attempt to make it a true second capital.Muhammad bin Tughluq greatly enlarged the empire, including regions deep in the south.He ordered a controversial transfer of the capital from Delhi to Daulatabad in the Deccan to strengthen control.This policy reflects his attempt to integrate north and south politically.Therefore, the best answer among the options is Muhammad bin Tughluq.

Verification / Alternative check:
Historical maps of the Delhi Sultanate show the greatest territorial extent under Muhammad bin Tughluq, stretching over most of the subcontinent. This supports the idea that he most clearly broke earlier political separation between north and south India.

Why Other Options Are Wrong:
Alauddin Khalji did expand into the Deccan but the question emphasises completed conquest and breaking political barriers, which fits Muhammad bin Tughluq more closely.
Ghiyasuddin bin Tughluq and Firuz Tughluq did not achieve comparable southern integration and are known more for other aspects of rule.

Common Pitfalls:
Many students are tempted to choose Alauddin Khalji because they remember his Deccan campaigns. However the phrase about breaking political barriers and the very large territorial extent point more precisely to Muhammad bin Tughluq and his ambitious capital shift to Daulatabad.

Final Answer:
The correct answer is Muhammad bin Tughluq.