The most basic difference between the two is that in union there are 15 players a side whereas league only has 13.
However, the major differences would be that in league once the attacking side has gotten 5 tackles they must either try (advancing the ball past the opponent's goal line and grounding it) or kick the ball away. If they fail to do one of these two things before being tackled, they have to turn the ball over to the opposition. In union however, the attacking side can continuously be tackled until either they lose the ball to the opposition or they commit an infringement.
One more difference I can think of is that in union, their scrums and line-outs (putting an out-of-bounds ball back in play) are important to the game whereas in league they do exist but are more incidental.
I hope that helps. :)
Odal's answer is the technical one (thanks, Odal, because I could never have given all that detail). This is the social answer:
Rugby Union is played more in the South of England, and in the posh schools. It's what they play in International matches, as the rest of the rugby playing world all follow Union rules. That's why so many (but not all) of the England Rugby Team are rather 'public school' (which means rich private school for our American friends - yes - I know it doesn't make sense).
Rugby League grew up in the North of England and was more for ordinary working men. Some Rugby Union people look down on it, but the northern League clubs are growing bigger and more popular, and there is a lot of cross-over between the Union and League clubs now. A fair number of the International players now spend the rest of their year playing League, rather than Union.What year did the football league start in the uk?
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