I've seen the same occurances on huge maps and many opponents. WW1 is exactly the right description.
Even had a weird situation where my little border skirmish with the Iroquis (They seemed to object to the action a spy took inside their territory...I don't know why they suspected me )
drew in the Aztecs who who were my MPP partner on my side.
Before it was all done, every country on the map went to war on one side or the other in that same turn. In the weirdest turn of events, one civ (the hapless Indians) first declared war on me, and then on my opponent as well, due to all the twisted diplomatic deals that had been brokered in the previous peaceful 500 years.
I have to admit I intentionally provoked the Iroquis just because I knew there was a massive web of MPP's involved, and I wanted to see how it all would play out.
Bill