Weird position of verb in sentence

Just today I wrote an answer to another question, that also deals with sentence structures. Please read this other answer for more details.

So, I can make it short here. The part that I marked bold and italics here is a subordinate clause:

Da wir am Wochenende viele von unseren Freunden zu einer Party eingeladen haben, müssen wir nun einen Großeinkauf machen.

Subordinate clauses only exist together with a subordinating conjunction like da, weil, als, wenn, obwohl, bevor, während, nachdem, damit, dass and ob, so some people argue, that this conjunction also belongs to the subordinate clause. But technically it is not. It is just the glue that joins it to the main clause.

This subordinate clause (now together with the subordinating conjunction "da") is one part of speech in the main clause. So, all the bold marked words in the next quote together occupy only one position in the main clause:

Da wir am Wochenende viele von unseren Freunden zu einer Party eingeladen haben, müssen wir nun einen Großeinkauf machen.

You can replace this 13 words long part of speech with just one word if you want (which of coarse changes the semantic meaning, but leaves the grammatical structure of the main clause unchanged):

Außerdem müssen wir nun einen Großeinkauf machen.

"machen müssen" is the predicate of the main clause:

Da wir am Wochenende viele von unseren Freunden zu einer Party eingeladen haben, müssen wir nun einen Großeinkauf machen.

Since the main clause is a statement, exactly one word from the predicate must stand at position 2 of the statement, and here this is the modal verb müssen. All other parts of the predicate (here only the full verb machen) must be put to the end of the sentence.

---

The predicate of the subordinate clause is eingeladen haben:

_Da wir am Wochenende viele von unseren Freunden zu einer Party eingeladen haben, _{müssen wir nun einen Großeinkauf machen.}

But since it is nit a statement, but a subordinate clause, all parts of the predicate must stand at the end of the sentence.