Complex sentence: The stress resulting from mounting academic pressure has now contributed to an increase in suicide in South Korea; for children aged 10 to 19 years old, where suicide is now the second most common cause of death in the country.
Split into simpler sentences: The stress resulting from mounting academic pressure has now contributed to an increase to the national suicide rates, particularly for children aged 10 to 19 years old. Suicide is now the second most common cause of death in the country.