Rugby Union has been much better at selling itself than League, but historically, especially in England, basically apart from the South West, Union was an establishment sport that has put League down and placed as many impediments as possible in its way (not been played in grammar or private schools; the armed forces; banning even amateur League players from Union). However, after 1995 that argument is redundant. In the 20 years since the two codes went open, Union has gone forward and League has regressed in my opinion. The Union World Cup has been, in my opinion, the catalyst for the growth in interest for the game.
France: Not sure how League has grown. I've worked for three French companies and only two people knew the game existed anymore. The Treizistes had some fine teams in the 50's that went to Australia in 51 and 55 that thrashed the Aussies and regularly beat the Great Britain team. That's now a thing of the past. Compared to Union there's a chasm between acceptance of the two codes as demonstrated by the huge amounts of money that Union gets from TV rights. I was at the Stade de France in 2009 for the French championship final between USAP and Montferrand. There was a full house of 82,000 people there. That would be a pipedream for League. Yes, they have a team in Superleague, but outside of the Catalans, it's a very minor sport in terms of publicity.
England: The schism of 1895 had the two codes going their separate ways. When I was a kid growing up in the 60's I always considered League to be the better code, but I don't anymore. The rules have been dumbed down. The scrum's been emasculated; the limited tackle rule has stopped the ability to apply pressure; consequently we have 13 backs playing the game because the forward skills of requiring props and hookers are no longer required. The heyday for League was the 1950's. The last time we beat the Australians in a home series was 1959, in Australia it was 1970 (due mainly to all time greats such as Malcom Reilly and Roger Millward being absolutely at the top of their game). Zilch since, although the Tours don't exist anymore since League went over to summer rugby in England. Then there was the embarrassment of the World Club Challenge over the weekend when Souths thrashed St Helens 39-0. Superleague's light years behind the NRL in my opinion. I found it embarrassing to watch.
Australia: It's the only place where League is dominant over Union. However, that popularity has meant that the NRL have done very little to expand the game beyond its own 'borders' of Queensland and NSW. They've rested on the success of its domestic competition. Yes, it's very popular in Papua NG and the Pacific Islands, but where else? Also, because of its dominance, the big deal in the NRL is State of Origin because they couldn't get a decent game against the English. To watch the NRL in the UK I have to subscribe to Premier Sports, which is bad marketing of the game by the NRL.
New Zealand: Still way below Union in the public consciousness, but something of a success story in terms of results. For a long time they were the 4th ranked team behind Australia, England and France. Now they are effectively the 2nd best team. That appears to be due to having a team in the NRL (Warriors) and many of its players ply their trade in the NRL as well. It's also gone from being a white man's sport in the 60's to now being almost exclusively Polynesians.
The nub of the argument for me is that League has done just about everything wrong in the last 20 years: rules, marketing, skills, internationals. I still have an emotional pull for the game, but I'm very disillusioned at the way things have turned out. The NRL is still worth watching, but Super League is poor.