Complex sentence: The youngest of the Australian communities is that of Perth, the capital of Western Australia, the formation of which in 1892 was due to the great influx of people into the western colony after the discovery of gold in the 1890s.
Split into simpler sentences: The youngest of the Australian communities is that of Perth, Western Australia. It was formed in 1892 as a result of the great influx of people into the western colony after the discovery of gold in the 1890s.