Complex sentence: First was the anti-war faction ("pacifists" loosely defined), who sought to keep the US out of the war at altogether and tended to view the conflict as a contest between British and German imperialism, both of which were regarded as equally immoral.
Split into simpler sentences: First was the anti-war faction ("pacifists" loosely defined), who sought to keep the US out of the war altogether. They tended to view the conflict as a contest between British and German imperialism, both of which they regarded as equally immoral.