Kleomenes came to the throne of Spa

Kleomenes came to the throne of Sparta around 520 BC. In a rivalry between Kleisthenes of Athens and Isagoras, he was called by Isagoras to help. Indeed Kleomenes forced Kleisthenes and his family to leave the country, but when he expelled five hundred more families and tried to revive the constitution, the Athenians revolted and besieged Kleomenes in the Acropolis, who immediately surrendered and left from Attica. He then assembled an army from Sparta and with allies marched toward Athens, without telling them that he wanted to install Isagoras as tyrant in Athens. But when the army came to Attica, the Corinthians learned the purpose of the expedition and abandoned the enterprise. The second king of Sparta, king Demaratos, who had joined the expedition refused also to go further and returned home and thus the expedition collapsed.
This gave the opportunity to Athens to attack the Thebans and Chalkidaeans, who were ravaging Attica and defeated them both.
In Sparta, after the kings quarrel, a new law was passed that in the future only one king would command an expedition. They also summoned the League and proposed to restore Hippias in Athens, who had been a friend of Sparta and had come from Asia for the meeting. Again Corinthians and other allies rejected the plan.
Around 505 BC, a war between Sparta and Argos took place, but the reasons are unknown.
In 499 BC, the Ionian leader Aristagoras came to Sparta to ask help in their revolt against Persia. Kleomenes refused and ordered him out of the city.
Kleomenes advanced into Argolis, but he failed to take Argos. He then asked ships from Sikyon and Aigina which unwillingly gave them and landed near Tyrinth. There he found, at a place called Sepea, which was between Argos and the sea, the Argive army. By gross carelessness of the Argives, he surprised them and defeated them. The Argives then tried to find refuge in the sacred grove of the Hero Argos. Kleomenes surrounded them and in a unthinkable for the Greek customs action, he set fire to the grove. Six thousand Argives lost their lives at that day, almost two thirds of the whole army (494 BC).
Kleomenes instigated Leotychides, the next heir in the Prokleid line of kings, to question the legitimacy of king Demaratos. To resolve the problem the Spartans went to the Delphi oracle, which declared Demaratos as an illegitimate king.
When later was known, that Kleomenes had bribed the oracle, they ordered him home, but he fled first to Thessaly and later to Arcadia, where he worked for a Pan-Arcadian alliance.
The Spartans called him again with promises, but when he arrived, he was attacked by the people, who following their old habit, they were hitting him in his head. The Ephors pronounced him insane. He committed suicide, having mutilated himself with a knife (488 BC).