What is the purpose of the United Nations? for countries to discuss problems and settle conflicts peacefully
for countries to impose their own laws on each other
to ensure countries follow established rules of war
to ensure countries use a democratic form of government

The first answer, "for countries to discuss problems and settle conflicts peacefully.

Explanation:

According to the UN, "...51 countries committed to maintaining international peace and security, developing friendly relations among nations and promoting social progress, better living standards and human rights."