Which of the following incidents was not associated with the year 1991?

Building of the Berlin wall

The correct answer is Option (1) - Building of the Berlin wall

The Berlin Wall symbolised the division between the capitalist and the communist world. Built in 1961 (construction also started in 1961) to separate East Berlin from West Berlin, this more than 150-kilometre-long wall stood for 28 years and was finally broken by the people on 9 November 1989. This event symbolized the end of the division between East and West Germany and marked the beginning of the reunification of Germany. It was a significant development in the end of the Cold War.

All the other 3 incidents: End of cold war, Disintegration of USSR and the Beginning of US Hegemony occured in 1991.