Concerned at the expense of maintaining the Falkland Islands in an era of budget cuts, the UK again considered transferring sovereignty to Argentina in the early Thatcher government. Substantive sovereignty talks again ended by 1981, and the dispute escalated with passing time. In April 1982, the Falklands War began when Argentine military forces invaded the Falklands and other British territories in the South Atlantic, briefly occupying them until a UK expeditionary force retook the territories in June. After the war, the United Kingdom expanded its military presence, building RAF Mount Pleasant and increasing the size of its garrison. The war also left some 117 minefields containing nearly 20,000 mines of various types, including anti-vehicle and anti-personnel mines. Due to the large number of deminer casualties, initial attempts to clear the mines ceased in 1983. Demining operations recommenced in 2009 and were completed in October 2020.