Complex sentence: He performed in Germany and Austria under the Nazi regime, but, while he made some appearances outside the country, including concerts under the baton of Bruno Walter in Amsterdam, he was unable to pursue an international career until his Covent Garden debut in 1947.
Split into simpler sentences: He performed in Germany and Austria under the Nazi regime, but, while he made some appearances outside the country, including concerts under the baton of Bruno Walter in Amsterdam. He was unable to pursue an international career until his Covent Garden debut in 1947.