The structure of local government in the United Kingdom underwent large changes in the 1990s. The system of two-tier local government introduced in the 1970s by the Local Government Act 1972 and the Local Government (Scotland) Act 1973 was abolished in Scotland and Wales on 1 April 1996 and replaced with unitary authorities. In England, some areas remained two-tier but many unitary authorities were created. No changes were made to local government in Northern Ireland.