The Americans' ability to inflict heavy casualties on the British during the Battle of Bunker Hill was primarily due to their advantageous defensive positions.

Positioned on Breed's Hill, colonial forces constructed strong earthworks and fortifications that provided significant cover and height advantage. This strategic setup allowed the Americans to effectively target British troops as they advanced, resulting in substantial casualties for the enemy. The use of these defensive positions not only showcased the tactical prowess of the colonial forces but also demonstrated their resolve to stand firm against a larger, more experienced army.