The 4-3-3 came with different strategies as demonstrated by the German team in 1972. Behind marking backs played a Libero (sweeper), who moved into the midfield position when the team won possession of the ball.
The 4-4-2 developed into a 3-5-2, since four defenders were only facing two forwards. One of the defender positions moved into the midfield position (since 1980).
L. van Gaal (coach of Ajax Amsterdam) developed in 1991 the dynamic 3-4-3, which could easily turn into a defensive 4-3-3, 4-4-2 or 3-5-2
(Please click here for Part I)