Complex sentence: The Nazi gun control theory is a counterfactual history that gun control was a significant component of the Third Reich's plans and that its that victims, especially Jews, could have more effectively resisted if they had been armed or better armed.
Split into simpler sentences: The Nazi gun control theory is a counterfactual history that proposes a connection between gun laws in Nazi Germany and the inability to effectively resist repression. The theory suggests that victims, especially Jews, could have more effectively resisted if they had been armed or better armed.