1. Why is the second tier called The Championship and the third tier called League 1?
Pretty much marketing. It used to be called Division 1, 2, 3, etc, but when the top division changed to the Premier league, there was a perceived gap between that is the next level down being division 2. So they changed it to the Championship at some point to drum up more support.
2. How can there be a ManchesterUnitedif there is a Manchester City?
The same way there is the New York Jets and the New York Giants.
3. Why do England and Wales split up for World Cup but are combined for league play?
They are still separate countries and have separate leagues. The exception are Cardiff and Swansea who joined the English leagues and have worked their way up from the bottom.
4. And while I'm at it, how many countries are actually over there on those two islands? I was always thought it was 2: Ireland and the United Kingdom of Great Britain and Northern Ireland. I only know that latter name because I was working with the British Navy a few years back and that's what I had to call them in a document I wrote.
Ireland, Northern Ireland, Scotland, Wales, England, Sealand!