The Eurodollar market first came into being in the 1950s when the Soviet Union's oil revenue -- all in US dollars -- was being deposited outside the US in fear of being frozen by US regulators. This resulted in a vast offshore pool of dollars outside the control of US authorities. The US government therefore imposed laws to restrict dollar lending to foreigners. Euro markets then became particularly attractive because they had fewer regulations and offered higher yields. From the late 1980s onwards, US companies began to borrow offshore, finding Euro markets an advantageous place for holding excess liquidity, providing short-term loans and financing imports and exports.
London was and remains the principal offshore market. In the 1980s, it became the key center in the Eurodollar market when British banks began lending dollars as an alternative to pounds in order to maintain their leading position in global finance. London's convenient geographical location (operating during Asian and American markets) is also instrumental in preserving its dominance in the Euro market.
