Step 1: Understanding the Disintegration of the Soviet Union
- The Soviet Union, a federation of multiple socialist republics, disintegrated officially on December 26, 1991, following years of political, economic, and social turmoil.
- This led to the formation of 15 independent republics, the largest of which was Russia.
Step 2: Analyzing the Options
- (A) 1990: Incorrect, while the Soviet Union was facing significant internal challenges, it officially dissolved in 1991.
- (B) 1991: Correct, the Soviet Union officially disintegrated in December 1991, marking the end of the Cold War.
- (C) 1992: Incorrect, this was after the official dissolution of the USSR.
- (D) 1993: Incorrect, the Soviet Union had already disintegrated by this time.
Step 3: Conclusion
The Soviet Union officially disintegrated in 1991, which is the correct answer.
\[
\boxed{\text{Correct Answer: (B) 1991}}
\]