Are the Marvel Netflix series (Daredevil, Jessica Jones, Luke Cage, Iron Fist) part of the Marvel Cinematic Universe or part of a universe that branched off after the events of the first Avengers movie (2012). I ask this question because in the Netflix series only the fight in Harlem (Hulk vs. Abomination) and the attack on Newyork (Chitauri invasion) are mentioned. Events thereafter such as the Triskelion collapsing (Captain America: The Winter Soldier) and Sokovia being lifted up into the air (Avengers: Age of Ultron) are never mentioned. Does anyone know an answer to this question?
Yes, they are part of the MCU, but only loosely. It's only been recently that any kind of connection has been made between the Netflix series and the movies
It's important to realize, though, that the Marvel Netflix shows are currently running several years behind the movies. In fact, Jessica Jones Season 2 was the first Marvel Netflix series to be set after the events of Captain America: Civil War, with liberal mentions of the Raft, the prison for "enhanced" individuals. That's why viewers tuning in to Luke Cage Season 2 expecting to see the impact of Avengers: Infinity War's ending were always destined for disappointment; Luke Cage was set in late 2016 or (at the latest) early 2017, meaning there were never going to be any tie-ins to Infinity War.
The tie-in is that the FBI is involved in enforcing the Sokovia Accords (remember that from Civil War?)
The key detail is that the FBI is responsible for policing some aspects of the Sokovia Accords in the United States. In Ant-Man and the Wasp, the FBI monitors Scott Lang to ensure he doesn't break his house arrest. FBI agents are also conducting a manhunt for Hank and Hope, who possess sufficiently advanced technology that they're viewed as in breach of the Sokovia Accords. This is an important detail; previously we'd only ever seen S.H.I.E.L.D. involved with the Sokovia Accords in Agents of S.H.I.E.L.D., but they'd been mostly concerned with identifying potential Inhumans and dealing with high-priority cases. Now we know that jurisdiction was presumably divided between S.H.I.E.L.D. and the FBI.
[I]it's safe to assume that Daredevil Season 3 will see Matt Murdock resume his vigilante activities. Such a vigilante would inevitably be viewed as a breach of the Sokovia Accords, although not a high-priority one - nobody actually knows the self-styled "Devil of Hell's Kitchen" actually has super-powers. Given that's the case, it's safe to assume the FBI would be called in to investigate the resurgence in vigilante activity in Hell's Kitchen. It's already been confirmed that Daredevil Season 3 has a strong FBI presence, with Wilson Bethel cast as a mystery FBI agent who plays a major role.