Good question.  First, we had to become an independent country...that happened in 1905.  Then building the nation from scratch was priority - and, naturally, an opera house was not first on the agenda for a very poor nation. It remained a dream. Then the war and occupation (1940 -45), and the rebuilding after the war. Always more 'important' buildings and projects to concentrate on. It must be said that opera has always been seen as elitist in Norway, so politically not easy to make it priority.    

About 20 years ago, it was finally decided that now is the time to build the opera. Then it took about 12 years of political wrangling to decide where it should be located, a few years of planning and building... And here it is.  

We have of course had opera before, but in a building not quite fit for purpose.