Niun-Shindan War

The Yin-Shindan War was the last of the wars traditionally included by historians in the larger conflict known as the Wars of Zhenian Transition, being fought from 1430 to 1438. It was strongly tied to the rest of the transitional conflicts experienced throughout East Tarsis, and in the political instability and border tensions created by the Third Zhu-Shindan War. The flight of many Zhu loyalists to the south in the Great Escape led to the formation of the Yin Dynasty, which claimed the Mandate of Heaven and direct succession from the Zhu, directly challenging the Shindanese claim over the Mandate and attracting the support of many Zhu loyalists and Wei refugees. With Shindan being initially unable to challenge the Yin due to the instability of their control over what had formerly been the northern territories of the Zhu, the Yin managed to consolidate their position, pacify the regions under the control, and to create a military that continued the reforms started in the last period of the Zhu.

The stabilization of the situation in both nations, and the defeat by Shindan of the last other possible claimant dynasty in the region inevitably led to conflict. The refusal of the Yin to submit to the Shindanese and to abandon their claim over the Mandate ended with a full-scale Shindanese invasion of the south, but the circumstances had changed radically since the last Zhu-Shindan War. The Yin banners were more than capable of fighting at the same level as the Shindanese forces, and the large numbers of former Zhu veterans and deserters who had been pressed into service allowed the Yin to limit the Shindanese numerical superiority. Political and economical stability at home also removed some of the biggest disadvantages that the Zhu had to face, and the first Yin emperor personally took command of his forces in the field.

The Shindanese eventually managed to break through the defenses on the southern bank of the Chang river and to press south, but their forces were weakened and were stopped in the Battle of Tianghai, 50 kilometers from the Yin capital of Tianjing. This victory allowed the Yin to push back, but their losses stopped them from further pushing north and taking advantage of Wei rebellions happening in Shindan at the time. The war ended with a return to the status quo ante bellum and a de facto recognition of the already existing borders, even if the two states refused to formally recognize each other, and the Treaty of Zhulhae was signed by the respective leading ministers of the two countries in their own names, without directly mentioning the two nations of their rulers.

The Yin-Shindan War had profound influences on the history of East Tarsis. The de facto Yin victory allowed the domains of the Yin dynasty to remain independent, eventually coalescing into the nation of Yinguo, and stopped the Shindan from conquering the entirety of what had once been the Zhu dynasty. For the Yin, this victory and the personal role played by the Yin Taizu Emperor were fundamental in strengthening their national identity and the popularity of the newly formed dynasty, while for the Shindanese monarchy, their failure to complete their conquests weakened their own position and sowed the seeds of military opposition. In an attempt to further its legitimacy, Shindan declared the formation of the Empire of Zhenia in the final year of the war, abandoning the Mandate of Heaven and claiming direct descent from the Zhen dynasty, which had a deep effect on the Tarsic philosophy of rule. The failure of the Treaty of Zhulhae to properly solve the tensions between the two nations firmly established Zhenia and Yinguo as rivals and enemies, a rivalry that would mark East Tarsis until 1570.