Trade unionism in the United Kingdom was a major factor in some of the economic crises during the 1960s and the 1970s, culminating in the "Winter of Discontent" of late-1978 and early-1979, when a significant percentage of the nation's public sector workers went on strike. By this stage, some 12,000,000 workers in the United Kingdom were trade union members. However, the election victory of the Conservative Party led by Margaret Thatcher at the 1979 general election, at the expense of Labour's James Callaghan, saw substantial trade union reform which saw the level of strikes fall. The level of trade union membership also fell sharply in the 1980s, and continued falling for most of the 1990s. The long decline of most of the industries in which manual trade unions were strong – e.g. steel, coal, printing, the docks – was one of the causes of this loss of trade union members.