Could someone explain this, please?

それは、求め、応え、集った３人の貴き神々が築いた新天地。

I kind of get it, except the "求め、応え、集った" part.
"It was a new universe built by three noble deities"... who did what exactly? orz I understand the individual meanings of these 3 words, but just somehow cannot figure out where they belong in this sentence contextually. It just seems so random. (Any established expressions involved?)

最初に相手を求めたのは、果たして。。。どちらか。

I have a hard time deciding what does "どちら" mean here. Is it "who" or "both"?