In a way, the ones before Modern Warfare would probably not really count as Call of Duty games anymore. I think the first kind of real one of the genre was Medal of Honor, and then the team left that developer and worked on Call of Duty. The first one really does mimic a bunch of Band Of Brothers so accurately, it’s scary. I remember play COD1 multiplayer and the rewatching BOBs and I’d approached that gun position where the germans were, and cleared out the area so many times exactly how they did it. But we’re talking games about games which are 17 years old here. I remember Stalingrad sniper duals, multiple Omaha beaches, Battle of the bulge, capturing the Reichstag and Eagles nest. All big historical moments. However, limited in their repetition.
It got a massive burst of popularity when COD: Modern Warfare came out. The series had kind of fallen out of favour by then. Previous to this it was all historical. But I think MW also came alongside a big update in the engine too. Battlefield may have eaten COD’s lunch after a while, I can’t remember, I stopped playing mutliplayer about then. But Modern Warfare took the crown back.