The Cold War was a state of political and military tension after World War II between the United States, and its NATO allies and others, and the Soviet Union and its allies in the Warsaw Pact. The Cold War was known as cold as it never escalated to full scale fighting between the two sides, but there were regional wars, known as proxy wars, which were supported by the two sides.
The first phase of the Cold War began within the first two years after the end of World War II in 1945. It lasted for decades, finally ending with the formal dissolution of the Soviet Union in December 1991.
During the Cold War, there was a nuclear arms race between the Soviet Union and the United States. This led many to fear that it would lead to a full-scale nuclear war. In 1955, when Marty McFly showed Doc Brown the tape of the DeLorean time machine experiment from 1985, Doc assumed that his future self was wearing a radiation suit due to fallout from atomic wars.
Over the course of thirteen days, between October 16 and October 28, 1962, there was a standoff between the United States and the Soviet Union over ballistic missiles deployed in Cuba. The Cuban Missile Crisis, also known as the October Crisis, or the Missile Scare, was broadcast on television worldwide, and was the closest the Cold War ever came to escalating to full-scale nuclear war.
On October 24, 1962, the Cuban Missile Crisis had been going on for nearly ten days, and many people thought the world would end that week. Colonel Lomax and the retired Lieutenant General Leslie Groves went to Doc Brown's mansion to offer Emmett Brown a large sum of money to invent a time machine, in order to prevent it from ever happening. Emmett Brown had impressed Leslie Groves during his time working on the Manhattan Project, who felt that Emmett was the most likely person to be able to develop such a device.
Emmett accepted the offer, as he needed funding for his inventions, and showed them his prototype time machine, the temporal field capacitor. It was only useful for sending objects into the future, as sending an object even a few minutes into the past caused a buildup of flux energy. If an object was sent any further back than that, the arrival of the object would overheat the capacitor and start an electrical fire.
Colonel Lomax was skeptical, and noted that they were seeking for a way to travel to the past, not the future. Emmett told them that with the right resources, he would be able to fix the problem in no time. The two men are interested, and Groves informs Emmett that he'll never have to worry about funding again.
After Lomax and Groves left, Emmett had worries that he could be ushering in an arms race through time, coupled with his regrets about ushering in the nuclear arms race of the Cold War through his participation in the Manhattan Project.
The next day, Emmett wrote himself a letter about his plans, and purposefully sent the letter back several months in the past, to August 1, when he knew that he and his dog, Copernicus, would be safe asleep in his fireproof garage.
The Brown family mansion burned down, and on October 24, Lomax and Groves came and left in the new timeline without ever talking to Emmett. They were told by Goldie Wilson, who was there handing out flyers for his campaign for district council representative, that the mansion had burned down months prior and that most people believed that Emmett had done it himself for the insurance money. Groves expressed his disappointment that Emmett Brown had become an insurance thief, and Lomax stated that they should leave, as he was not the type of man that they would want to hire.