Do i manually need to point out every sentence that back me up?

One is enough. You cant though. Almost as if it is a lie you just keep repeating.

I just linked a reliable source that backed me up.

Then quote the part. You cant though. Almost as if it is a lie you just keep repeating.

And i explicitly said that the US have become multicultural.

You explicitly said: "The USA and other american nations were forged on the basis of immigration and multi-culturalism."

If you have realized you were wrong, just say so.

The top one is common knowledge

"What can be asserted without evidence can be dismissed without evidence" - Hitchens

Well yea missed a word there.

And it was "downtrend", correct?

If it turns out the founding fathers were absolutely opposed to multikult, how would that change your stance?