"what was the chief reason for colonial discontent just prior to the first shots? "

The chief reason for colonial discontent just prior to the First shots was the stationing of British troops in cities. By the mid-1770s, though, the relationship between the American colonies and their British rulers had become so tense, so poisoned, so regarded as by disbelief and resentment that the once seemingly indestructible bonds of empire were on the verge of dissolution. And in the spring of 1775, the first shots were fired in a war that would sooner or later win America its independence.