Which of the following best describes the purpose of a nation’s boundaries?

from what I found it should be

to prevent other countries from invading Territory

A border ( boundary, frontier ) is a real or superficial line that separates geographic areas.

A border can separate countries, states, provinces, counties and towns. A government of a region can only create and enforce laws within its borders.

Borders are necessary for :

- to keep out invaders. This refers to disputes over once common territory, in times of war, and to stop illegal immigrants entering the country.

-to protect resources, ethnic, religious or economic communities.

-to prevent crime. This implies mostly to human trafficking and smuggling.