Wikipedia claims that after the Battle of Granicus, Alexander the Great sent 300 Persian armors, with the message "Alexander, son of Philip, and all the Greeks except the Spartans, give these offerings taken from the foreigners who live in Asia".
Now I know from other posts that Sparta was a shadow of its former military power (if they ever had any).
What was the purpose then of this "gift"?, was it a Diplomatic overture? was he mocking them? inviting them? did it even happen or have any meaning at all?
The gift was to Athens, as a form of requital for what the Athenians had suffered during the Persian Wars (that is, the razing of the city by Xerxes in 480 BC). The reason why Alexander specified that the gift was from all the Greeks except the Spartans was that all the Greeks except the Spartans had submitted to Macedonian hegemony and joined the League of Corinth, sending contingents to Alexander for his campaign against Persia. The army with which he crossed to Asia contained men from all the states of the Greek world except the Spartans, who had stubbornly refused to sign the treaty and join the League because doing so would imply a recognition of the independent status of Messenia, over which they claimed ownership. As a result, the Spartans were explicitly excluded from all the dedications Alexander made.