There was an old belief in English football that was especially prominent in the 80s and 90s that stated that all good teams, especially title-winning teams, are built from the back. A strong defensive structure is established first and then everything else is added to that foundation.
Whether that is in fact true is somewhat debatable, particularly given the offensive explosion of the modern game. But an underlying sentiment of defensive stability being important does still remain. You cannot win much with a leaky defence. The New York Red Bulls were the best defensive team in MLS last season.