The Seven Years' War left the British severely overstretched in terms of their imperial commitments. This meant that they had to maintain a permanent army on American soil—mainly to keep Native American tribes at bay—and that they had to pay for it with increased taxes on the American colonists.
Both of these measures were deeply unpopular with Americans, who, as well as resenting the payment of additional taxes, regarded a standing army as a potential instrument of tyranny in the hands of colonial authorities. In those days, standing armies were relatively rare. Armies tended to be called up as and when they were required, say for a specific conflict.
But the idea of having a permanent standing army was an anathema to the long-standing tradition of liberty which had developed over centuries in England and which had crossed the Atlantic to North America. The American colonists, inheritors of this tradition, genuinely believed that, far from protecting them from Native Americans, British soldiers were there to keep them in line and if necessary use force to crack down on any expressions of dissent.