Aside from low birthrates and high deathrates, what can cause a country's population to decline?

Emigration from a country.

Which one is the underlined word?

Although this may be the opposite of what you think i will say it anyway. you were brought into this world for a reason and you still have soo much ahead of you. not everybody has an opportunity of living a great life, but it doesn’t give you a reason to end everything. somebody in the world loves you, and imagine what you would do to them if you left forever.