I wasn't even at the climax, but I was having all the characters converge at once on the time and place they were all interested in, in order to collide.
And it took me two days to settle down to it. First to arrange the sequence so that they actually collided in succession, since in prose you can't actually depict two things at once. Then to track out how they collided, and collided, and collided. . . .
Still haven't gotten to the end. One faction is sneaking off from a second, and they're about to run into a third.
Well, one reason to add more than two factions to your story is to complicate the plot. I have to say that it succeeded in this case.