Answer:
A. Union leaders rushed into attacks against larger Confederate forces.
Step-by-step explanation:
One reason for the failure of the Union's Peninsula Campaign was that Union leaders rushed into attacks against larger Confederate forces. This led to a series of costly and unsuccessful battles, including the Battle of Gaines's Mill and the Battle of Malvern Hill, in which the Union suffered heavy losses. The Union's decision to attack larger Confederate forces without proper planning and preparation was a major contributing factor to the campaign's failure.