Complex sentence: Since the 1990s when the Paul Keating ALP government enforced a policy of mandatory detention of unauthorised arrivals, non-citizens arriving by boat without a valid visa were detained until they were either granted a visa, or deported.
Split into simpler sentences: Since the 1990s the Paul Keating ALP government enforced a policy of mandatory detention of unauthorised arrivals. All non-citizens arriving by boat without a valid visa were detained until they were either granted a visa, or deported.