The New Zealand rugby team, the All Blacks, have been the dominant force in world rugby over the last 100 years. Over that period they have win ratio of 75%, no other team has achieved that in any sport, they are simply the most successful sports team ever, even compared to teams that have been playing for a much shorter time.
All this has been done on very limited resources, as you can see below there were only 27,000 adult male rugby players in New Zealand in 2011, England had 166,000, over 6 more players per position. England is far and away the richest union, although the Americans could probably stump up cash when needed and they too have more players than New Zealand. South Africa has 4 times as many adult male players as New Zealand.