Final answer:
The British feared the loss of their alliance with the Iroquois as it was crucial for Britain to maintain the support or neutrality of the Iroquois in the war against France. The Iroquois' strategic contribution and political influence were significant factors in the American Revolution.
Step-by-step explanation:
The British feared a failure of their alliance with the Iroquois Confederacy during the American Revolution predominantly because Britain could not afford to go to war with France without the assistance and/or neutrality of the Iroquois (C). The Iroquois, being a major political force in the Northeast for more than a century, had strong military capabilities, and their alliance with Britain brought four out of the six nations into the fray, ensuring a divide within the Confederacy itself. The neutrality or allegiance of the Iroquois was crucial since most of the Indian tribes supported the British due to concerns over American colonial expansion and loss of lands.
The involvement of the powerful Iroquois significantly affected the strategic positions during the war. With figures like Mohawk Joseph Brandt advocating for the alliance with the British, and nations like the Mohawk, Cayuga, Seneca, and Onondoga joining them, the British were able to solidify their position and hoped to minimize the support to the American cause, as failing to maintain this alliance could potentially sway the outcome of the conflict.