They were fighting against Mussolini and also against the Nazis.
Appeasement
Many Greeks stated that Greece was more advanced than Persia.
Marshal Pietro Badoglio (1871-1956) became Prime Minister on July 25, 1943, the day after the Fascists voted no confidence in Mussolini. He remained Prime Minister until June 18, 1944, and organized the Kingdom of Italy forces against Mussolini's forces and Germany.
The request for a signed photo of Mussolini was made by American actor and filmmaker Orson Welles. He was denied the request, as Mussolini's regime had a policy against sending autographed photographs to non-Italians. Welles later recounted this anecdote, highlighting the peculiarities of his experience during his visits to Italy.
against the Greeks because he was the king of Persia
Yes, the Spartans did fight against the Greeks. They fought them in the Peloponnesian War.
They were fighting against Mussolini and also against the Nazis.
Benito Mussolini
some Greeks rebelled against he and helped there fellow Greeks in the fight for Asia
The Greeks fought against the Persians in the movie 300 starring Gerard Butler
communism
Not against any international law, but people (morally / ethics) will probably not like you for it.
He joined forces with Germany in WWII against the US and allies
the Greeks
no idea
The Greeks stood their ground and fought for their freedom against the Persians. Their victory caused the Greeks many lives.