For more than five centuries these two nations existed as one on the peninsula, being ruled as a dynasty called the Choson. Then in 1910, Imperial Japan annexed the peninsula and ruled it as a colony for 35 years. In 1945, when Japan surrendered during WWII the Korean peninsula was split into two separate zones. THe US-controlled the Southern region and the Soviets controlled the Northern regions: this North and South Korea was born.
Due to the growing tensions during the Cold War, two separate governments were formed the peninsula has been split in two ever since. The north attempted to unify the whole peninsula under a communist rule which caused the 1950 Korean wars. Technically speaking the two nations are still at war even if now actual combat and skirmishes are rare.
So after five centuries as one nation, you would think that their cultures would still be quite similar. However, the separation of over 70 years apart has caused some strange developments. Surprisingly a key change is around around language, the language has diverged so much that 45% of the defectors from North Korea have problems understanding the Korean spoken in South Korea. In fact, 1% have admitted they do not understand it at all!
The cultures have shifted massively too, the North Korean way of life now rests on top of the image of self-reliance and the propaganda spread that their one-man ruler is the greatest. However, most defectors do not actually flee the politics. The main reason given is the economic problems of the nation: famine and poverty. A majority of people surveyed that were able to escape actually miss home.
Despite all the surveillance and terror used to sustain the regime, it has been found that a lot of television watched in North Korea is actually South Korean dramas. So in that sense, it looks like people are willing to take a risk to keep certain cultural links alive.