Complex sentence: They disengaged, and met up again a few kilometers away in the Siege of Shioda castle at 8--12 September, where Takeda forces has taken Wada and Takashima, then slaughtered the entire garrison as a warning to the remnants of Murakami forces in 10 September.
Split into simpler sentences: They disengaged, and met up again a few kilometers away in the Siege of Shioda castle, where Takeda forces had taken Wada and Takashima, on 8--12 September. There they slaughtered the entire garrison as a warning to the remnants of Murakami forces on 10 September.