Complex sentence: The Easybeats and The Bee Gees were probably the best-known acts from this era to gain success outside Australia, but by the mid-Sixties there were hundreds of bands working in Australia and New Zealand.
Split into simpler sentences: The Easybeats and The Bee Gees were probably the best-known acts from this era to gain success outside Australia. By the mid-Sixties, there were hundreds of bands working in Australia and New Zealand.