What was the main subject of writings Alexander Solzhenitsyn?

The writings of Aleksandr Solzhenitsyn primarily focus on the experiences and consequences of the Soviet regime and its totalitarian nature. His works extensively explore themes of political oppression, human rights violations, and the resilience of the human spirit under extreme circumstances. Solzhenitsyn's influential literary contributions shine a light on the horrors of the Soviet Gulag system and the broader oppressive realities of the Soviet Union during the 20th century.