US$1.7 billion on the construction and remodeling of Cuban factories and industry. Between 1981 and 1984 Cuba also received approximately US$750 million a year in Soviet military assistance. When Mikhail Gorbachev came to power in March 1985, the Soviets continued to consider Cuba as an important Cold War propaganda tool. Economic investment and trade in Cuba were at their highest. In 1985, trade with the Soviets accounted for over 70% of Cuba's entire trade. Both nations continued to collaborate on projects in the sciences, technology, sports, and education. However, throughout the Gorbachev era diplomatic relations cooled until the end of the Soviet Union in 1991 terminated Soviet-Cuban relations. Heightened tensions best characterized diplomatic relations between Cuba and the Soviet Union throughout the Gorbachev era. The introduction of his Soviet reforms of perestroika and glasnost and his "new thinking" on the foreign policy set off an economic crisis in the Soviet Union, opened up the Soviets and their allies to increasing internal criticism from dissidents, and sparked an ideological conflict with the Cuban regime. 1985–1989 The Soviet Union faced a varying array of problems when Gorbachev took power after the death of General Secretary Konstantin Chernenko in 1985. However, Gorbachev's attempts at reforms not only provoked the strengthening of a vocal opposition frustrated over the pace of reforms but also placed the Soviets at odds with Cuba. The transition during perestroika towards market reforms weakened the Soviet ruble and resulted in a reduction of basic subsidies and widespread shortages of basic goods, a loss of jobs, and decreased productivity. The economic difficulties spread to other areas of Eastern Europe and other Soviet satellites, such as Cuba. In essence, perestroika progressively undermined the Soviet Union's ability to live up to its economic commitments to Cuba. In 1986, Castro embarked on his own set of reforms, which was called the "rectification of errors" campaign. Castro intended for the reforms to forestall or to eradicate any reformist ideas spreading in Cuba prompted by radical political and economic reforms in the Soviet Union or elsewhere in Eastern Europe. The Cuban policies and perestroika were diametrically opposed and highlighted the unravelling of the Soviet-Cuban relationship. The effects of glasnost on political criticism and discussion in the Soviet Union further strained the Cuban-Soviet alliance. After Castro bashed glasnost during a joint Soviet-Cuban conference in Havana in 1988, the Soviet elite became more critical of Soviet foreign policy