Short answers, pulled from the story.
Marvel Studios was formed in 2005 to produce its own films independently and distribute them through Paramount Pictures. The first MCU film, Iron Man, released in 2008, began Phase One of the franchise.
Kevin Feige envisioned combining characters like the Avengers team in a shared universe similar to the one created by Stan Lee and Jack Kirby for Marvel Comics in the 1960s. Feige became studio chief in 2007 and led the creative committee that preserved artistic integrity.
Phase One consists of Iron Man (2008), The Incredible Hulk (2008), Iron Man 2 (2010), Thor (2011), and Captain America: The First Avenger (2011). Phase Two comprises Iron Man 3 (2013), Thor: The Dark World (2013), Captain America: The Winter Soldier (2014), Guardians of the Galaxy (2014), Avengers: Age of Ultron (2015), and Ant-Man (2015). Phase Three begins with Captain America: Civil War (2016) and includes Doctor Strange (2016), Guardians of the Galaxy Vol. 2 (2017), Spider-Man: Homecoming (2017), Thor: Ragnarok (2017), Black Panther (2018), Avengers: Infinity War (2018), Ant-Man and the Wasp (2018), Captain Marvel (2019), Avengers: Endgame (2019), and Spider-Man: Far From Home (2019).
Disney agreed to acquire assets from 21st Century Fox in December 2017 and finalized the transaction on the 19th of March 2019. This acquisition saw the return of film rights for Deadpool, the X-Men, and the Fantastic Four to Marvel Studios.
Marvel Studios began contracting their actors for multiple films, including signing actor Samuel L. Jackson to a then-unprecedented nine-film contract. The studio also ensured directors were open to the idea of the shared universe and willing to include connective material.