I revised my thesis a little, here it is (it might be a little too long, not quite sure)
Soviet foreign policy was predominantly successful at achieving its primary aim of protecting the revolution and strengthening the USSR however its secondary ideological aim of exporting worldwide communist revolution was ultimately rendered unsuccessful due to the conflicting nature of the dual objectives.
When I said conflicting nature, I was also thinking incompatibility could work too. Which one is the better word to use?