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.

The French and Indian War (the seven years war) between the English and the French was fought 'in the backyards' of the British colonials, resulting in colonial resentment towards the French as well as their sovereign nation.  Great Britain won the war, however at great cost.  King George's 'piggy bank' was bankrupted and so he looked towards his colonies for its replenishment.  The status-quo mercantilistic policies and the salutory neglect between the crown and her colonies for so many years were suddenly thrown into a lion's den.  The crisis between the crown and the colonies was steeped in the rights of Englishmen, going back to Magna Carta 1215.  Although many of the colonists had already developed an 'American' reality they were true to their enlightened beliefs.  The Seven Years War pitted the reality of a bankrupted monarchy against the ideology of its foreign subjects.

Main reasons why the French and Indian War/ 7 Years War causes the crisis between the colonies and Britain:

1.  This is the biggest one: it causes the British government to go too deep in debt.  So they want money to make up for that.  That's why they start trying to tax the colonies and trying to crack down on smuggling and stuff like that.  So the war leads them to try to control the colonies more than ever before and the colonies don't like that.

2.  Takes the French out of North America so the Americans don't have to worry about getting swallowed by France if they become independent.

3.  Allows Americans from different colonies to get to know one another and see that they have things in common.  Before that, they might as well have been from different countries so there was no way they'd work together to become independent.