Just read the act!
Because it didn’t!
You don’t understand the word corporation.
One could say the US (even the colonies) has always been a “corporation” it has the right to own property and make contracts, to receive gifts and legacies, to sue and be sued, and, in general, to perform legal acts through representatives. The District of Columbia Organic Act of 1871 changed nothing other than the governing arrangement of the then municipalities in the District.
When you’re a cabal of international bankers, and you want to pull a dirty trick, what do you do to hide it?
They changed “The Constitution for the united states of America” to “THE CONSTITUTION OF THE UNITED STATES OF AMERICA.”
Does changing words (like for), and adding capitalization, change the legal meaning in a document?