His is the next question,

just filling in a bit of:
the pertinent details, which includes why it was important to the development of Athenian politics and empire. as requested.

When Cleisthenes saw Hippocleides beating time with his legs in the air, he could bear it no longer. 'Son of Tisander' he cried, 'You have danced away your marriage.'
'I could hardly care less', was the cheerful reply. Hence the common saying, 'It's all one to Hippocleides.'
Cleisthenes then decided to give his daughter Agarista to another, to Megacles the son of Alcmaeon.

Such is the story of the Trial of the Suitors, and this was the way in which the Alcmaeonidae came to be talked of throughout Greece. The issue of this marriage was Cleisthenes, (named after his grandfather) who reorganized the Athenian tribes and instituted Democracy in Athens. A second son of Megacles was Hippocrates, who became the father of another Megacles and another Agarista, who married Xanthipupus the son of Ariphron. This Agarista dreamt during her pregnancy that she gave birth to a lion, and a few days later became the mother of Pericles.

Herodotus - Book Six - 133 (Hippocleides at Sicyon)