Hi I was wondering could help me with this question... :-)
Why did it seem improbable that the thirteen colonies would come together and unite in a common bond? What past events made this seem like an unrealistic expectation?
Off the top of my head, I can answer your first question.
The 13 colonies were used to operating as individuals, so they were concerned that they wouldn't have any rights if there was a national government. The Articles of Confederation (and, later, the Constitution) guaranteed that while the national government was more powerful, the states would still have their own power, too.