What led to their creation in the first place?

Re this question, there have been a few posts in this sub describing the origins of the football codes & the (English) FA. Re the history of the various professional leagues, if you don't get responses here, perhaps x-post to /r/Soccer or check the leagues' respective websites or even Wikipedia (all of the league articles include some history).

• Can anybody explain when and how rugby, football, soccer, etc. developed?

• When football(soccer) was first created, were there any tournaments held between competing teams? If there were, were there matches between different countries?

• How legit is the theory that the word soccer was invented in the United Kingdom?