If you have a continuing interest in the subject, I recommend that you take a look at the development of the Supreme Court's commerce clause case law from the Civil War onwards. You need not agree with the results, but you would benefit from an understanding of how this area of law developed.
The Government Printing Office has an online edition of their annotated guide to the Constitution, which you may find at the following link: GPO Annotated Constitution
"It is not intended to say that these words comprehend that commerce, which is completely internal, which is carried on between man and man in a State, or between different parts of the same State, and which does not extend to or affect other States. Such a power would be inconvenient, and is certainly unnecessary."
And some do not.