When the Democratic People 's Republic of Korea ( DPRK , informally North Korea ) and the Republic of Korea ( ROK , informally South Korea ) were created in 1948 , this line became a de facto international border between the two countries . It was also one of the most tense fronts in the Cold War . Upon the creation of the Democratic People 's Republic of Korea ( DPRK , informally North Korea ) and the Republic of Korea ( ROK , informally South Korea ) in 1948 , it became a de facto international border and one of the most tense fronts in the Cold War .