North to south
The border does not have a particular name, but most of it is along the YALU RIVER.
The Yalu River separates the countries of North Korea and China. Your answer is China.
The Mississippi River
the river that flows along the western border of the district is the kwilu river
The original US-Mexico border was defined by the Sabine River north from the Gulf of Mexico to the 32nd parallel north (32°N), then due north to the Red River, west along the Red River to the 100th meridian west (100°W), due north to the Arkansas River, west to its headwaters, north to the 42nd parallel north (42°N), and finally west along that parallel to the Pacific Ocean. This border also includes Texas, which was considered a rebel province at the time.
Top right (North-East) along the river Rhine on the German border
The Rio Grande River flows along the border of Mexico and the United States of America. It flows along the border of Texas.
The Missouri River starts in Montana, flows through North Dakota and South Dakota, then along the border between Nebraska and Iowa, then flows across Missouri and into the Mississippi river near St. Louis, Missouri.
The two rivers that form the northern border of North Korea are the Yalu River and the Tumen River.
The Missouri River flows from the Rocky Mountains in Montana, through North Dakota and South Dakota, along the border between Iowa and Nebraska, then through Missouri to the Mississippi river near St. Louis, Missouri.
West Virginia, Ohio, Illinois, and Indiana form the northern border of Kentucky, along the Ohio River.