King Seonjo of Joseon, who reigned from 1567 to 1608, focused on improving the lives of common people and rebuilding the nation after the corruption and chaos of Yeonsangun and Jungjong's reigns. He restored the reputations of scholars unjustly executed in previous purges and denounced corrupt aristocrats. Seonjo reformed the civil service examination system to include politics and history, gaining respect from the populace and enjoying a brief period of peace.

However, King Seonjo's reign saw the emergence of significant political divisions, leading to the East-West feud between 1575 and 1592. This division originated from the scholars he appointed, who split into two factions: the conservative Western Faction led by Sim Ui-gyeom and the reform-minded Eastern Faction led by Kim Hyowon. The Western Faction initially gained favor due to Sim's royal connections and support from wealthy nobles. However, their hesitance on reforms led to the rise of the Eastern Faction. This faction further split into the Northern and Southern factions, with differing degrees of reformist agendas.

These political divisions weakened the nation, particularly affecting military preparedness. Despite warnings from neutral scholars like Yi I about potential threats from the Jurchens and Japanese, the factions failed to strengthen the military, believing in the continuation of peace. This lack of preparedness had dire consequences, as it coincided with the expansionist ambitions of the Jurchens and the Japanese, eventually leading to the devastating Seven-Year War and the rise of the Qing dynasty in China.

King Seonjo faced challenges from the Jurchens in the north and Japanese leaders like Oda Nobunaga, Toyotomi Hideyoshi, and Tokugawa Ieyasu in the south. The Japanese threat escalated after Hideyoshi unified Japan. Despite the growing danger, factional disputes in the Joseon court prevented a unified response. Delegates sent to assess Hideyoshi's intentions returned with conflicting reports, further fueling controversy and confusion. The Easterners' dominance in the government led to the dismissal of warnings about Japanese military preparations. This factional infighting, coupled with the 1589 rebellion of Jeong Yeo-rip, significantly contributed to Joseon's unpreparedness for the impending Japanese invasions.