Conversation so far:
What was Black Wednesday?
When the British government was forced to withdraw the pound sterling from the European ERM
What is the European Exchange Rate Mechanism?
A system to reduce exchange rate variability and achieve monetary stability in Europe, in preparation for Economic and Monetary Union and the introduction of a single currency, the euro

Question: Why was the country forced to exit the ERM?
Self-contained rewrite: Why was the UK forced to exit the ERM?