The eastern coast is steep and rugged with few islands. The mountain range slopes more gently to the west and ends in a network of estuaries and tidal flats. Rivers that flow into the Yellow Sea and the Korea Strait are generally slow, while those flowing into the Sea of Japan are short and swift due to the mountains. The climate on the Korean Peninsula is influenced predominantly by winds from Siberia and the East Asian monsoons. There is a noticeable variation in climate between coastal and inland areas.
Winter is characterised by substantial snowfalls, particularly in northern and mountainous regions.
The Korean people are generally considered to be descendants of nomadic Mongolian and central Asian tribes who migrated to the Peninsula around 4,300 years ago. Their civilisation is among the oldest in the world. Despite historic ties and contacts with China and Japan, the population is remarkably homogeneous, both ethnically and linguistically, and has a distinctive cultural heritage. The average population density is nearly 200 people per km2, concentrated mainly in the lowland plains of the western part of the country and along the eastern coastal strip. The likely explanation for this rapid fall is the introduction of stringent birth-control policies in the 1970s.