Complex sentence: When James was convicted and transported to Australia as a convict, it was very rare for convicts or their family to attain permission, or even afford to join them in their exile, so Martha and his children were left in England to fend for themselves.
Split into simpler sentences: When James was convicted and transported to Australia as a convict, it was very rare for convicts or their family to attain permission, or even afford to join them in their exile. So Martha and his children were left in England to fend for themselves.