It wasn't created to oppress black people. It was created because Hamilton, Madison, etc., didn't trust a direct democracy. Read the Federalist Papers. It's in there.

The Founders left it up to the states to determine who was able to vote. In Pennsylvania and New Jersey, black men could vote. In New Jersey, so could single women.

However, in 1807 New Jersey restricted voting to white men, and in 1838 so did Pennsylvania.

One reason I think black men could vote for so long in Pennsylvania - it was founded by Quakers who were also some of the earliest abolitionists. They believed in universal brotherhood. They were often the most active on the Underground Railroad. But the demographics of the state changed...