Why did the 13 colinies break away from britan and become the united states?
(i totally forgot),

Mostly religious freedom and economic prospect.

The 13 colonies were tired of Britain's strict laws and policies regarding them, especially their taxation laws. The colonies had no representation in Parliament (British gov.) but were being taxed as if they did. This is where the phrase "no taxation without representation" comes from. (This is all off the top of my head, let me know if I can better explain anything!)