Why did Japan and the United States begin diplomatic negotiations in March 1941? Were they successful? Explain

On December 8, 1941, the United States Congress declared war on the Empire of Japan in response to that country's surprise attack on Pearl Harbor the prior day. It was formulated an hour after the Infamy Speech of President Franklin D. Roosevelt. Japan had sent a message to their embassy in Washington, but because of problems in decoding and typing out the very long message – the high-security level assigned to the declaration meant that only personnel with very high clearances could decode it, which slowed the process – it was not delivered to the U.S. Secretary of State until after the Pearl Harbor attack. Following the U.S. declaration, Japan's allies, Germany and Italy, declared war on the United States, bringing the United States fully into World War II.

Yes - The turning point in the Pacific war came with the American naval victory in the Battle of Midway in June 1942. The Japanese fleet sustained heavy losses and was turned back.