Complex sentence: The king heard of Handel's abilities, and wanted him to train as a future court composer, but Handel's horizons had been broadened by his sojourn in Berlin and he was developing his own ideas for his future.
Split into simpler sentences: The king heard of Handel's abilities, and wanted him to train as a future court composer. However, Handel's horizons had been broadened by his sojourn in Berlin, and he was developing his own ideas for his future.