One reason the colonists had difficulty coming together to revolt against britain is because they

Lacked a unified army, is the right answer.

Explanation:

All the thirteen colonies of the United States had a militia comprised of farmers and untrained individuals. Every colony had very little similar factors, in lack of which, the armies of the colonies could not be united. Accordingly, to fight against the British troops suggested fighting without any force for the colonies. At the time of revolt against Britain, the leaders of the colonies asked workers and farmers to join the army to possess a theft to the enemy, however, the lack of unity among colonies proven to be a serious problem for the colonies against the British.

letter d is correct.