The hypothetical scenario of Jiró Nitta unifying Japan in the early Muromachi period (1336-1573) presents a fascinating counterfactual history, drastically altering the course of Japanese development. His success hinges on several key factors, all of which would necessitate significant deviations from historical events.

Military and Political Maneuvers: Nitta's initial success against the Ashikaga shogunate stemmed from his strong military support, particularly amongst the warrior class who were discontented with the Ashikaga's ascension. For a complete victory, he would need to have:

• Secured unwavering loyalty from his allies: Maintaining the cohesion of his forces throughout a prolonged campaign would be crucial. Historical accounts suggest internal conflicts and shifting alliances weakened his position. To avoid this, a more effective strategy to manage ambitions and secure loyalty from key daimyo (feudal lords) would be necessary. This could involve significant concessions, strategic marriages, or even the implementation of a more centralized feudal system.

• Defeated Ashikaga Takauji decisively: Takauji's military acumen and the resources at his disposal were formidable. A decisive victory, eliminating Takauji and his forces early in the conflict, would have been critical. This may have required a superior strategy, unforeseen tactical advantage, or even the demise of key Ashikaga generals through assassination or other unforeseen events.

• Neutralized or incorporated the Go-Daigo Emperor's support: While initially supported by Emperor Go-Daigo, their relationship was complex and ultimately fraught with tensions. Nitta's success would have required a tighter alliance or at least the Emperor's neutral stance, preventing the Emperor from shifting his support to Ashikaga Takauji, as happened in reality.

• Effective control and governance of conquered territories: The sheer size of Japan would have presented immense logistical challenges. Nitta would have needed a robust administrative system, a well-trained bureaucracy, and a clear plan for integrating conquered territories into a unified nation. This contrasts with the decentralized nature of the feudal system at the time.

Social and Economic Impacts:

• A centralized government: A successful unification under Nitta would likely have resulted in a more centralized government, potentially delaying the onset of the Sengoku period (Warring States period) characterized by intense feudal warfare. This could mean a different path towards the unification under Oda Nobunaga, Toyotomi Hideyoshi, and Tokugawa Ieyasu centuries later, or possibly the development of a completely different political structure.

• Economic development: A unified Japan under Nitta might have seen accelerated economic development, due to improved trade routes, increased stability, and the implementation of consistent policies. This could have led to a stronger economy, potentially impacting Japan's international relations and its future engagement in trade with other nations.

• Cultural impact: The cultural impact is difficult to fully predict. A different ruling dynasty would likely have influenced the evolution of art, literature, and religious practices. The focus and emphasis on certain cultural traditions could have been significantly altered, resulting in a unique cultural landscape.

• International relations: A strong, unified Japan under Nitta could have altered its relations with China and Korea. A powerful centralized state would have been a formidable player in East Asian politics, influencing the balance of power and potentially leading to different alliances and conflicts.

Potential Challenges and Downfalls:

Despite these positive potentials, Nitta's unified Japan would still face challenges. Maintaining the loyalty of the powerful daimyo and preventing rebellions would be an ongoing struggle. The sheer scale of administration in a feudal system would be a constant drain on resources and potentially lead to dissatisfaction amongst the populace. Internal conflicts could still arise, possibly due to succession disputes or challenges to his authority.

Conclusion:

The counterfactual of Jiró Nitta successfully unifying Japan in the early Muromachi period offers a compelling glimpse into an alternate history. While a unified Japan under his rule would have brought significant changes in terms of governance, economics, culture, and international relations, it's crucial to acknowledge the inherent instability and challenges associated with maintaining a large, unified feudal state. The success of such a feat would depend on factors beyond mere military prowess, necessitating strong political acumen, effective administrative capabilities, and a deep understanding of the complexities of Japanese feudal society. The resulting Japan would be profoundly different, possibly avoiding the chaos of the Sengoku period but facing different challenges in maintaining its unity and stability. It would be a Japan shaped by a very different kind of leader and a different set of priorities, a path diverging significantly from the historical narrative we know.