Final answer:
Japan gained control of southern Manchuria and recognition of its rights to Korea after the Treaty of Portsmouth, bolstering its imperial power and regional dominance.
Step-by-step explanation:
Japan benefited from the Treaty of Portsmouth in several ways after the end of the Russo-Japanese War. The treaty acknowledged Japan's right to Korea and awarded Japan control of southern Manchuria. This victory and resulting territorial gains significantly increased Japan's sphere of influence in Asia. Furthermore, the treaty facilitated Japan's rise as a significant imperial power, allowing it to consolidate its position in East Asia. By gaining recognition as the sole power in Korea, which it later annexed, and taking over Russia's sphere of influence on China's Liaotung Peninsula, Japan expanded its empire and increased its resources and strategic advantages in the region.