The United Nations, while strong in some areas, is notably weak in others.
The UN is a voluntary organization where each country more or less agrees to respect the independence and sovereignty of each of its country members.
The UN does not have binding power to force any country to do anything that that country does not want to do.
The sovereignty of a country is considered sacred and it cannot be overruled by the UN.
This lack of binding power is probably the UN’s biggest weakness.