Haeso

Haesŏ, or Haeseo, is a region of Korea that occupies what is now North Hwanghae and South Hwanghae provinces of North Korea, as well as Baengnyeong Island and Ongjin County of South Korea. The region once hosted the Hwanghae Province of the Joseon period.

The name of the region, Haesŏ, means "West of the Sea", in reference to the region being to the west of Gyeonggi Bay, the portion of the Yellow Sea offshore of Incheon and Ganghwa Island.

Joseon and Korean Empire periods
From 1392 to 1910, the House of Yi (or "House of Ri" ( Munhwa'ŏ : 李氏朝鮮/리씨 조선) in North Korean) ruled over the entirety of the Korean Peninsula. The modern provinces of Korea were established in the 15th century. Hwanghae Province was originally formed in 1395 as Punghae Province (豐海道/풍해도 punghae-do), then was renamed to Hwanghae (黃海道/황해도 hwanghae-do) in 1417 by taking the first syllables of the provinces two principal cities: Hwangju and Haeju.

Contemporary history (1910 – present)
In 1910, Korea was annexed into the Empire of Japan, and its administrative divisions were rearranged. Hwanghae Province was reorganized into Kōkai-dō, with Kaishū (Haeju) serving as its capital.

Since 1945, most of Haeso has been under the jurisdiction of North Korea, while only several islands off the coast of South Hwanghae province are under the jurisdiction of South Korea. In 1954, Hwanghae Province was divided into the current North Hwanghae and South Hwanghae provinces.