Just more information on Nick Fury's appearances in the Silver Age
In 1959 Khruschev toured the USA. He incited Eisenhower, the FBI, and the American public with his confrontational and arrogant speeches. Eisenhower was supposed to reciprocate the following year with a tour of Soviet Russia, but the Russians shot down their first U2 spy plane flying over Moscow on a spy run. Khruschev was outraged and cancelled the invitation to Eisenhower to tour there. Then sent Sputnik over America, telling the US , "We can send Nukes to America". The USA was panicked by the prospect, as Sputnik flew over like a shot across their bow. The USA thought they had a Nuke advantage with 50 B52 Bombers at ready to send Nukes to the USSR but now this was the COLD WAR.
Then in 1961, Super Heroes appeared in Marvel Comicbooks. Story after story was of the Cold War in the books. The SH's were in the Cold War right from the beginning. Then they did a book called Sgt Fury and the Howling Commandoes (from an idea Kirby had in his notes in 1959, about a rugged soldier he thought of doing). 3 issues later of this series, these heroes of WWII met Reed Richards in their book in WWII, and you see Marvel introduced Nick Fury to the New Marvel Universe. Then Fury appeared in modern times in Fantastic Four issue 21. Then in Sgt Fury issue 11, Captain America and Bucky appeared with the HC, another introduction into the Modern New Marvel, because nobody introduced Cap and Bucky into the 1950's War comics at Atlas, at all, so why now? My interpretation is because Nick Fury, the WWII hero, who was more a hero than Super Heros in tights, was necessary to be there in the COLD WAR as well as SH's.