Complex sentence: This unpopularity was also encouraged by Russia which believed autocratic king to be a threat to its interests however Russian support to his opposition did not go unnoticed and from Gustav III and was one of the reasons why he thought the war as inevitable.
Split into simpler sentences: This unpopularity was also encouraged by Russia, which believed an autocratic king to be a threat to its interests. However, Russian support for his opposition did not go unnoticed by Gustav III, and was one of the reasons why he thought of the war as inevitable.