There was no Athenian empire at the battle of Marathon. Athens fought there with one minor ally Plataia.
Athens developed an empire 50 years later from the anti-Persian alliance known as the Delian League.
They killed each other.
The batte of Marathon was between the Athenian people or Athens and the greatest empire of that time Persia.
They were defending their city from an attempt by Persia to instal an expelled Athenian tyrant to rule them.
The Battle of Marathon, August/September 490 BC, gave Greece a victory over Persia.
It demonstrated to the Greek city-states that the Persian Empire was not unstoppable. It gave the Athenians great confidence in their abilities. It conviced Persia that it needed to take over mainland Greece to stabilise the western part of its empire.
Marathon was not a war, it was one battle in a 50-year war between Persia and the Greek city-states. The most important battles were Salamis, Plataea and Mycale. The significance of Marathon is that it was the first time that the Persians were defeated, and this Athenian victory showed to the other Greek city states, after nine years of Persian victories, that the Persians could be beaten.
In ancient times, Athens (and other Greek allies) secured one decisive victory over its traditional enemy, Persia, on a coastal plain called Marathon. Occurring in 490 B.C.E., this battle was won by the Greeks against a much larger force and ended a Persian invasion-threat.
Persia mounted a punitive expedition against Eretria and Athens for interfering in the Persian empire. Eretria was captured and the Persians then moved on to capture Athens, landing at the Bay of Marathon 26 miles north of the city. The Athenian army fought it out with them there.
Persia provided The Spartan league with the money to build a war fleet which could outmatch the hitherto superior Athenian fleet.
Persia provided The Spartan league with the money to build a war fleet which could outmatch the hitherto superior Athenian fleet.
Persia had a king, not an emperor. The Persian king Darius I was at home in Persia when the battle of Marathon took place, so he was not killed at Marathon. Darius the Great died of natural causes 14 years after Marathon.
Persia sent an expedition to Athens to reinstal an Athenian ex-tyrant to stop it causing trouble within the Persian Empire. The expeditionary force fought it out with the Athenian army on the Plain of Marathon. The Persians lost.