Thank you for the very comprehensive answer, Sak, and yes - it all made perfect sense! :D

I suppose we can't ever be certain of why Teotihuacán suddenly took more than a commercial interest in the Maya, unless it was just a muscle-flexing exercise by an increasingly influential power. There used to be the conception (and you'll still see it repeated) that Teotihuacán was a society of farmers and traders and not particularly militaristic until its later years, but I believe that view is now generally agreed to be down to wrong interpretations of Teotihuacáno iconography, and that the city in fact had a strong military sector from its earliest periods.

Just another comment on the Teotihuacán-Maya connection - I hadn't realised until recently, when I was reading an article on the Hunal Tomb, that the founder of the Early Classic period dynasty of Copán, K'inich Yax K'uk' Mo', had also "arrived" from Teotihuacan in a similar manner to Siyah K'ak's "arrival" at Tikal, and that later Cópan kings were very proud of their Teotihuacano heritage!