Jingnan campaign in the context of "Ming dynasty"

The Shanhai Pass (simplified Chinese: 山海关; traditional Chinese: 山海關; pinyin: Shānhǎi Guān; lit. 'Mountain Sea Pass') is a major fortified gateway at the eastern end of the Great Wall of China and one of its most crucial fortifications, as the pass commands the narrowest choke point in the strategic Liaoxi Corridor, an elongated coastal plain between the Yan Mountains foothills and the Bohai Sea, which is the only easily traversable landway between North and Northeast China. It is located in present-day Shanhaiguan District, Qinhuangdao, Hebei province, on the east bank of the Shi River, with defensive walls stretching from the Yan Mountains all the way to the shores of the Liaodong Bay.

Throughout Chinese history, garrisons around the pass served as frontline defensive outposts against raids and incursions into the North China Plain by various non-Sinitic ethnic groups from the Northeast (also known as Manchuria since the 19th century), including the Dongyi, Donghu (Xianbei and Wuhuan), Khitan and Jurchen (Manchus). The current Shanhai Pass was built during the early Ming dynasty as the easternmost fortification of the Ming Great Wall, and was extensively reinforced after Yongle Emperor moved the capital from Nanjing to Beijing following the Jingnan campaign, making it the most important defensive barrier in all of China, as it shielded the heartland region around the imperial capital. The pass' strategic location dictated that without mounting a costly direct siege, the only way an invading army can get past the pass' defense was to circumvent it around the north through a few treacherously narrow mountain passes deep within the Yan Mountains, which would make it very difficult to maintain supply lines and thus any sizeable invasions. This defensive significance therefore earned the pass the famous nickname "Greatest Pass Under Heaven" (天下第一关).

The Jianwen Emperor (5 December 1377 – 13 July 1402), personal name Zhu Yunwen, was the second emperor of the Ming dynasty, reigning from 1398 to 1402. Zhu Yunwen's father was Zhu Biao, the eldest son and heir apparent of the Hongwu Emperor, the founder of the Ming dynasty. Zhu Biao died in 1392, after which the Hongwu Emperor named Zhu Yunwen as his successor. Zhu Yunwen ascended the throne after the Hongwu Emperor's death in June 1398.

Upon his accession, the Jianwen Emperor immediately began revising the Hongwu Emperor's reforms, with the most significant change being the attempt to limit or eliminate the power of princes who were sons of the Hongwu Emperor. Zhu Di, the most powerful of these princes, rebelled against the Jianwen Emperor in 1399. He did this under the pretext of acting against allegedly corrupt court officials who had influenced the Emperor, following the Emperor's order for the imprisonment of Zhu Di's own followers. This sparked a civil war known as the Jingnan campaign, which Zhu Di framed as an effort to eliminate disorder. In 1402, Zhu Di captured the capital of Nanjing, and the imperial palace was burned to the ground. Even though three bodies were found at the burnt palace and were later announced to be those of the Emperor, his wife, and their eldest son, rumors of the Emperor's survival and refuge in a Buddhist monastery emerged. Zhu Di ascended the throne as the Yongle Emperor. He abolished the Jianwen Emperor's reforms and declared his reign illegitimate, thus abolishing the Jianwen era and extending the era of Hongwu to 1402. It was not until 1595 that the Jianwen Emperor's era and imperial title were restored by the Wanli Emperor.

The Yongle Emperor (2 May 1360 – 12 August 1424), personal name Zhu Di, was the third emperor of the Ming dynasty, reigning from 1402 to 1424. He was the fourth son of the Hongwu Emperor, the founder of the dynasty.

In 1370, Zhu Di was granted the title of Prince of Yan. By 1380, he had relocated to Beijing and was responsible for protecting the northeastern borderlands. In the 1380s and 1390s, he proved himself to be a skilled military leader, gaining popularity among soldiers and achieving success as a statesman. In 1399, he rebelled against his nephew, the Jianwen Emperor, and launched a civil war known as the Jingnan campaign, or the "campaign to clear away disorders". After three years of intense fighting, he emerged victorious and declared himself emperor in 1402.