Final answer:
General McClellan left behind 30,000 members of his army to protect Washington during his Peninsular campaign.
Step-by-step explanation:
During his Peninsular campaign, General McClellan was forced to leave 30,000 members of his army behind to protect Washington. This decision was made to ensure the safety of the nation's capital in case Confederate forces launched an attack. Leaving these troops behind was a strategic move to maintain a defensive position and prevent a potential loss of the capital.
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