 Complete the following phrase:  In the summer of 1941, Nazi Germany invaded the Soviet Union and drove into the large landmass of Russia and Ukraine on three fronts. The southernmost drove through the Caucasus with the objective of capturing the petroleum fields and reserves in Baku, Azerbaijan. By autumn, the German Wehrmacht had pushed far into the regions and was nearing the outlet of the northern Caucasus. In order to prevent a possible link up between Iran, whose leader Reza Shah Pahlavi harbored pro-German leanings, the Allies launched a joint mission to 