Complex sentence: Superman races to the Gulag, but upon arrival he is struck down by Captain Marvel who also causes a breach in the Gulag, freeing the population, thus inciting war between Wonder Woman's Justice League and the metahuman prisoners.
Split into simpler sentences: Superman races to the Gulag, but upon arrival is struck down by Captain Marvel. This causes a breach in the Gulag, freeing the population, and inciting war between Wonder Woman's Justice League and the metahuman prisoners.