I'm not sure which three specifically you're looking for, but here are three major causes of the revolution:
1) Taxation without representation This was a big deal to many colonists, especially because they were being taxed a large amount: large enough to help pay off the debt from the French and Indian war. The fact that they did not have a say in the amount that they would be taxed and how rubbed some of them off the wrong way.
2) The Boston Tea Party and the Intolerable Acts The Boston Tea Party was definitely a huge event in American history. This act of rebellion again Parliament's acts caused major backlash when Parliament issued the intolerable acts, made to punish them. Among other things, it closed the Boston harbor and took away their form of self government
3) Pro Independence Propaganda Many founding fathers and influential writers such as Patrick Henry and Thomas Paine wrote pieces that called for the colonies to become independent from British rule and even went as far to call British government a "tyranny". They made many persuasive arguments. Benjamin Franklin's "Join or Die" cartoon is also another good example.
I really hope this helps and I hope these were the three you were looking for!
