In the face of economic crisis and the growing influence of Solidarity, and under pressure from the USSR, General Jaruzelski decided on a violent solution. On 13 December 1981 Martial Law was introduced in the People's Republic of Poland. Several thousand opposition campaigners were interned, and strikes were crushed with the help of the army and special riot police units. On 16 December nine miners were killed in the Wujek Coal Mine. Many members of the opposition and underground trade-unionists were sentenced to prison terms, others were forced to emigrate. Martial Law, which was officially lifted in July 1983, had not resolved Poland's problems. The Polish economy still could not emerge from the crisis; opposition against the government did not diminish, but was kept up by the Pope's subsequent pilgrimages, in 1983 and 1987 and award of the Nobel Peace Prize to Lech Wałęa, Solidarity's leader (1983), none the less Solidarity structures had significantly weakened, and many succumbed to intimidation. Nevertheless the trade union continued to operate illegally under Wałęsa's leadership, which was reflected in the regular publication and distribution of several hundred clandestine periodicals and bulletins. Solidarity campaigners received support from the Church, which kept its strong position in society. By 1983 the scale of the repressions as well as of the opposition activities was relatively moderate compared to the earlier phase.