The Third Cold War is a conflict during the events of Call of Duty: Black Ops III. It was a conflict that began 12 years after the Second Cold War and 46 years after The First Cold War. The conflict resolved around the Winslow Accord, Common Defense Pact, Nile River Coalition and 54 Immortals.
After The Second Cold War, loyalties were called into question and with several major European nations leaving the already disintegrating EU, what was left of them had to reluctantly admit Russia into the EU in order to survive eventually forming the Common Defense Pact.
This had a major effect on the United States and their influence on European geopolitics. In 2037, with their influence essentially gone in Western Europe, they turned towards the Pacific region where they had formed the Winslow Accord. The CDP considered this to be an act of aggression and so it sparked a new cold war.
In 2059, the NRC-Egyptian Conflict had occurred, with both nations facing severe droughts the Africans resorted to stealing from the Egyptians and war was declared. With the Winslow Accord publicly backing their Egyptian allies whilst the CDP covertly supported their NRC allies, forming a proxy war.