The main reason why Congress worked to keep a balance between the number of slaveholding states and free states is because they wanted to avoid war breaking out between the North and the South. They tried to do this through a series of compromises that ultimately failed.
Answer: The Battle of Jumonville Glen
Explanation: Historians generally consider the Battle of Jumonville Glen as the opening battle of the French and Indian War in North America, and the start of hostilities in the Ohio valley.