Light did not answer Kyran at once— not because the former did not know who organized the war, but because it was a very complicated subject to discuss.
The War of the Sovereigns was not organized by one person or an association. It was an affair that would occur after certain requirements were met. As for who would announce its commencement, there was no one. Sovereigns were only aware that it would start soon by instinct.
Regarding the requirements, there were two that needed to happen. First, the alignment of every plane in the Lower Realm and second, the number of Sovereigns it birthed.
Alignment of every plane did not mean a linear formation of every plane, but their 'time' and magic law.