The Southern States were underrepresented in the Senate compared to the House by the initial apportionment in the Constitution, represented at very close to the same ratio in each House in the apportionment for the 1790 Census (largely reflecting that they had been overrepresented relative to population, in the House, in the Constitutional apportionment), and substantially overrepresented in the Senate compared to the House after the 1800 Census.
They were well aware of the imminent demographic trends and acted accordingly.
> History and facts matter.
Indeed they do, but the history and facts aren't on the side of “the Southern States had large initial and expected future populations as counted for apportionment in the House and, so by-State representation in the Senate was contrary to, rather than designed to serve, their regional interest.”
That's orthogonal to the concerns of small population states, in 1787, when the Connecticut Compromise was adopted.
What's more, the results of 1790 and 1800 Censuses didn't impact support or opposition to that compromise, as they hadn't been performed yet.
>by-State representation in the Senate was contrary to, rather than designed to serve, their regional interest.”
Which is the flip-side of the coin to what I said.
No. It had to do with Connecticut, New Jersey and other small population states who wouldn't have ratified the Constitution unless there was state representation (as we have in the Senate) to balance out the representation by population (cf. The Connecticut Compromise[0]).
The southern states had (or expected to have) large populations, and as such, wanted representation by population.
History and facts matter.
[0] https://en.wikipedia.org/wiki/Connecticut_Compromise