Complex sentence: The American war aim was to detach the war from nationalistic disputes or ambitions, after the Bolshevik disclosure of secret treaties between the Allies, which discredited their claims that Germany was the sole power with aggressive ambitions.
Split into simpler sentences: The American war aim was to detach the war from nationalistic disputes and ambitions after the Bolshevik disclosure of secret treaties between the Allies. The existence of these treaties tended to discredit Allied claims that Germany was the sole power with aggressive ambitions.