replaced the ECU 1:1 at the exchange rate markets, on 1 January 1999. Between 1979 and 1999 the D-Mark functioned as a de facto anchor for the ECU, meaning there was only a minor difference between pegging a currency against the ECU and pegging it against the D-Mark. The eurozone was established with its first 11 member states on 1 January 1999. The first enlargement of the eurozone, to Greece, took place on 1 January 2001, one year before the euro had physically entered into circulation. The zone's next enlargements were with states that joined the EU in 2004, and then joined the eurozone on 1 January in the mentioned year: Slovenia (2007), Cyprus (2008), Malta (2008), Slovakia (2009), Estonia (2011), Latvia (2014), and Lithuania (2015). All new EU members having joined the bloc after the signing of the Maastricht Treaty in 1992 are obliged to adopt the euro under the terms of their accession treaties. However, the last of the five economic convergence criteria, which need to be complied with in order to qualify for euro adoption, is the exchange rate stability criterion. This requires having been a member of the ERM for a minimum of two years without the presence of "severe tensions" for the currency exchange rate. Irish pound breaks parity with sterling To participate in the European Monetary System, Ireland chose to break the Irish pound's parity with sterling in 1979, because the UK had decided not to participate. (The Irish Central Bank had maintained parity with sterling since the foundation of the state in 1922. "It was only in the 1970s, when high inflation in the UK threatened price stability in Ireland, that alternatives were seriously considered".) Sterling's forced withdrawal from the ERM The United Kingdom entered the ERM in October 1990, but was forced to exit the programme within two years after sterling came under major pressure from currency speculators. The ensuing crash of 16 September 1992 was subsequently dubbed "Black Wednesday". There was some revision of attitude towards this event given the UK's strong economic performance after 1992, with some commentators dubbing it "White Wednesday". Some commentators, following Norman Tebbit, took to referring to ERM as an "Eternal Recession Mechanism", after the UK fell into recession in 1990. The UK spent over £6 billion trying to keep the currency within the narrow limits with reports at the time widely noting that the controversial