Some Systems...

To summarize the development of tactical formations- in the earliest days Association Football was based on all out attack (although the scores from those days, rather than suggesting goal-fests, have a modern familiarity).
Attacking moves were launched by long balls from the backs and individual dribbling and rushes by the massed forwards.
The 2-2-6 of Queens Park, Scotland and the Royal Engineers was about advancing the ball with more subtlety and certainty through passing (the Combination Game).
This was refined in the 1880s when one of the two centre forwards withdrew into midfield, creating the pyramid (2-3-5) and developing the role of the centre half.
The  centre half was a  fulcrum who had a key role in launching attack when in possession and countering  the opposing centre forward when in defence. They were the playmakers of the era.
The emphasis  remained firmly on attack, which was largely dependent on the two wide forwards taking on the full backs, getting to the by line and sending crosses into the box.
The 1925 change in the offside law was designed to favour the attacking side as clever and coordinated defences were exploiting the 'three defenders' rule to close down the space available. In the last season of the old offside law 2.5 goals per game were scored in the Football league. In the first season of the new rule this rose to 3.4. Paradoxically though this development led to the emphasis in tactical thinking shifting towards the defensive aspects of the game.
The origins of the third back are obscure and controversial- and I argue that it is simplistic to attribute its introduction solely to Chapman and Buchan seeking to redress the balance following the change in the offside law- and a 7-0 drubbing at Newcastle. However, analysis of Chapman's contribution to tactics shows that sound defence was the foundation on which all his innovations were based. 
From this point on tactical developments began to be about stopping the opposition playing, and Italy's Vittorio Pozzo stated this quite openly.

The back 3 in the WM (3–2–2–3)- the centre half drops back slightly behind the full backs and becomes responsible for the offside trap and adopts the role of 'stopper'.

 Pozzo introduced a successful system known as Metodo. Pozzo, who referred to the formation as sistemo, utilized the tirelessness of  Monti in a centro mediante position. When Italy were in in possession he retained his position as a creative midfielder, but would drop back to neutralise the opposing centre forward without becoming a pure defender. The withdrawal of the inside forwards into midfield to compensate for the lessening of the centre half's creative endeavours created a 2–3–2–3 set up.
Criticism of Monti's deployment in this position had echoes of the criticisms levelled at the third back in England- his role in the 1934 World Cup was described as being that of a spoiler.

The back 4 of the verrou.

Another significant rearrangement comes right at the end of our period. The Verrou-the bolt - saw the addition of a fourth defender. This system, introduced in Switzerland by Karl Rappan, set the stage for post war defensive developments. It suited teams with limitations (it has been referred to as being about  the right of the weak). Greater emphasis was placed on cohesion rather than  reliance on skill. It was also reflexive, with positions responding to the state of play, with players dropping back when out of possession, but the  most important development was the introduction of the ultra defensive central defender- the bolt.