What problem did the United States and Russia still have to solve after the Cold War Apex

Preventing nuclear war

Nuclear Weapon reduction and proliferation

Explanation:

One positive result of the end of the Cold War was a reduction in nuclear weapons. Under Bush the U. S. and USSR negotiated and implemented the START I and START II treaties, which limited the number of warheads each country could possess to between 3,000 and 3,500. The other problem they faced was to prevent nuclear proliferation, as authotities fear that more countries with nuclear material would increase the possibility of a nuclear war.