Final answer:
Joseph Stalin's first Five-Year Plan focused on industrialization and agricultural reform. It aimed to rapidly industrialize the Soviet Union and increase agricultural production through collectivization.
Step-by-step explanation:
The main focus of Joseph Stalin's first Five-Year Plan was industrialization and agricultural reform. The plan aimed to rapidly industrialize the Soviet Union by increasing iron and steel production, building new power stations, and developing cities dedicated to specific industries. The plan also sought to reform agriculture through collectivization, which involved moving from individual farms to large state-run farms. Despite the implementation challenges and resistance from peasants, the plan significantly increased industrial capacity in the Soviet Union.