the answer is 10 years
No the federal government controls the trade between the states.
To prevent European expansion in the Americas
No the federal government controls the trade between the states.
The constitution should prohibit the states from participating in the international slave trade.
to regulate intrastate trade, as allow by the constitution
This is exactly what happened when the original colonies were governed by the Federalist Papers, which led to the Continental Congress and the founding of the Constitution for the nation. Each state would not take the other states money and trade between the states broke down. To alleviate the problem the states came together to work out the problems under the auspice of the Convention of States. What they ended up getting was the Constitution that radically changed trade, economic trade and international trade.
The United States Constitution protected the slave trade for twenty years. This protection was not to expire prior to the year 1808. After January first of that year, laws could take effect to end the slave trade in the United States.
By giving Congress the power to regulate trade within the states
The Constitution vested Congress with the authority to regulate trade with other nations, between the states, and with Native American Tribes in the Interstate Commerce Clause (Article I, Section 8, Clause 3).
By giving Congress the power to regulate trade within the states
The British blockade hindered trade between Germany and the United States in 1915.