What was Braddock’s Blunder?

The Braddock expedition, also called Braddock's campaign or, more commonly, Braddock's Defeat, was a failed British military expedition which attempted to capture the French Fort Duquesne (modern-day downtown Pittsburgh) in the summer of 1755 during the French and Indian War.

Explanation:

Perhaps his most serious error was the failure to heed intelligence reports offered by Indian scouts; Braddock regarded the natives as inferiors and refused to deal with them. General Edward Braddock commanded bravely – four horses were shot out from under him – but was mortally wounded and died several days later. Washington had the general's body interred under the road over which the soldiers and wagons passed in retreat, hoping to spare it from desecration.

an era of negotiation.

is that an answer to your question?