(Getting some stunningly idiomatic Sibelius in 1971, in Japan!)
It sounds altogether odd to speak of a Sibelius revival. Sibelius is one of the facts of 20th century music, with great champions to play his music all through the century. If any composer didn't need a revival, it was Sibelius. Yet toward the mid-century marker, Sibelius's fortunes looked to be dipping in an altogether serious way. In the arid climate of postwar Europe, Sibelius was considered a sentimental nostalgist. It was only in the late century when Finland, a country of 5.4 million emerged as as a state which seemed to produce a greater number of amazing classical musicians than many countries ten times its size. Like Hungary in second quarter of the century, there was something in Finnish training that seemed to cement achievement in great talent. And just as all those Hungarians made sure Bartok got his due, all those Finns supported Sibelius. The very first conductor of the 'Finnish invasion' to emerge on the world stage was Paavo Berglund.
(Berglund in mid-70's Dresden. Making perhaps what's still the greatest non-Czech recording of Smetana's Ma Vlast.)
It doesn't do Berglund's talent much justice to claim that he was a mere Sibelius authority, though that will inevitably be how he's remembered - he recorded the Sibelius Symphonies 3 1/2 times and in 1970 made the first ever recording of Sibelius's only truly large-scale work, the Kullervo Symphony. But he will probably be remembered as much for how he played Sibelius as that he played him at all. Conductors as diverse as Eugene Ormandy, Colin Davis, Leonard Bernstein, and Herbert von Karajan played him in the grand manner of the Romantics, with almost Teutonic heaviness and Russian emotionalism. By today's standards, their tempos were quite broad and the phrases stretched to their breaking point. Berglund wiped the palate clean of all Romantic excess: the tempi on the whole much faster, dynamics far more understated, and phrasing far less flexible. This was a cooler, more concentrated Sibelius for a more understated era of music-making, perhaps it was also closer to how the composer saw his own music. Was Berglund the greatest of all Sibeleans? He's certainly in the running, but there are other approaches to the music that work equally well - I prefer mine fleet, but with a bit more romantic drama and flexibility, which you get especially well from classic giants like Koussevitzky, Kajanus, Stokowski, Beecham, and Barbirolli. Among the more contemporary names, it's a style probably best represented by Neeme Jarvi and Simon Rattle.
(The Seventh Symphony in London with the BBC Symphony. Berglund's way with Sibelius was particularly appropriate for this symphony.)
For all the specialty in Sibelius, Berglund was a general practitioner - making some legendary recordings of Shostakovich, Smetana, and Vaughan Williams in his day. His temperament was naturally reserved - with a large helping of volatility by all accounts, which perhaps goes a bit of the way to explaining the weird mix of restraint and explosion that his performances could inspire. One moment, a Berglund performance was the very definition of forbearance, the next moment it could explode in an awe-inspiring example of orchestral fireworks and passion (the fireworks never more on display than in his recording of Vaughan Williams's Fourth Symphony with the Royal Philharmonic).
(En Saga in Bournemouth, where he was a particularly beloved chief conductor.)
It is a shame that Berglund never achieved more fame in his time. Aside from in Britain, where he held a variety of posts, the major world centers of music never seemed to consider him in the front rank. He was part of a generation that seemed particularly attracted to flashy performers, and Berglund was the polar opposite of flash. But if the cool but consistent talents of Mackerras, Dohnanyi, Blomstedt, Haitink, and Zinman could be recognized on the international stage, however belatedly, why not Berglund?
(The Oceanides. Probably Sibelius's most underrated tone poem, I've never heard it done better than Berglund did it.)