Sparta
Sparta becaus they were more disciplined and knowledgeable when it came to war
The Spartan alliance defeated the Athenian alliance in 404 BCE after the Athenian fleet was destroyed at Aigospotamai. Subsequently, Athens and Sparta fought as allies and opponents on several occasions. There was no final defeat. Each waned as a power after the mid 3rd Century BCE.
It provided the Spartan alliance with the money to get a sea fleet to match and defat Athens' hitherto superiority. With its fleet destroyed, Athens was confined within its walls, could not import food, and was starved into surrender.
The Athenian empire was stronger at sea, the alliance led by Sparta was stronger on land.
Persian Empire.
On paper at least, almost all long-term alliances are defensive - and this applied to the Triple Alliance, too. Incidentally, in WW1 Italy fought against the "Triple" Alliance ...
As Greeks, their cultures were very similar. Their alliance was for self interest - Sparta aided Athens, and Athens reciprocated.
delian league
N.a.t.o
The Warsaw Pact
The address of the National Alliance Of Preservation Commissions is: Po Box 1605, Athens, GA 30603-1605
After WW II, in the era of the Cold War, the defensive military alliance was (and remains) NATO, the North Atlantic Treaty Organization.
ITALY refused to give support
NATO
I would say if a country has a defensive treaty alliance with another country it would mean that they would not fight with that country, but also that if the country they had the alliance with were to be attacked by another country that they would help to defend them.
The Delian League
Athens.