Pls be understood a bit more.
The second sentence, –international and American championship titles–
international title –one title American championship–another title
so both create –titles, two of subjects connected with –And.
So, you need a plural verb—were.
However, what I understand from your question that is you need many morphological matters to understand verb+subject topics.
Pls you should check it out a morphology of grammar book, I mean you need a book that analyses many grammatical matters or you needn’t only a plain grammar book.