Solution:The chronological sequence of Cold War events is based on their actual historical timeline:A. Vietnamese intervention in Cambodia – Began December 25, 1978, when Vietnam invaded Cambodia to overthrow the Khmer Rouge regime.
D. Fall of the Berlin Wall – Happened on November 9, 1989, marking the symbolic end of the Cold War divide.
C. Gorbachev becomes the President of the USSR – He formally became President on March 15, 1990 (though he was General Secretary from 1985).
B. Unification of Germany – Completed on October 3, 1990, bringing East and West Germany together.
Arranged in ascending order (earliest to latest): A (1978) → D (1989) → C (1990) → B (1990).