What mistaken tactic did the british follow that led to the tragic defeat of braddock as he marched his troops toward fort duquesne?

The failure was blamed to the European Tactic. Braddock was adamant in using the tactic but failed to carry it out properly. Ultimately, his failure to gather a light infantry which could have given the signal of the enemy’s attack led to the defeat. 

is this like a kind of true or false question?

the speech revealed that eastern european countries were no threat to their neighbors, which led to the creation of the truman doctrine i think this might be correct.