How did The Empire of Japan annex Korea? (mirror)

Original description:
How did The Empire of Japan annex Korea?

The Japan-Korea Treaty was a significant point in relations between the two nations and was signed back in 1876 as Korea began its pull away from China. The goal was to grant Japan new trade rights with Korea, opening three ports and also giving Japanese nationals in Korea extraterritorial rights. From that point on, slowly, Japan gained more and more control over Korea until the full annexation