Religious exclusivism asserts that one religion is true and that all others are in error.
It has two forms;
Absolute Exclusivism; Asserts that one religion is true and that all others are in error and one must be born into the religion to be a true adherent.
Relative Exclusivism; Asserts that one religion is true and that all others are in error therefore conversion is mandatory. Examples are Christianity and Islam.
The Decree of Diopithes 430 bce forbade the worship of and belief in Gods other than those of the Olympian pantheon recognised by the Athenian Polis. The introduction of other Gods was treated as asebeia or impiety and was punishable by death. The Philosophers Anaxagoras, Protagoras, Socrates, Stilpo, Theodorus of Cyrene, Aristotle, and Theophrastus were accused of impiety under this decree. Socrates was found guilty of the charge of introducing new Gods and condemned to death by drinking Hemlock.
Antiochus IV Epiphanes Selucid ruler of Israel born ca.215; died 164 bce. Antiochus decided to Hellenize the Jews by ordering the worship of Zeus, when they refused Antiochus sent an army to enforce his decree.
According to Herodotus the Caunians a Greek people who claimed to have originated in Crete and settled in Asia Minor worshipped the Olympian Gods exclusively. "They determined that they would no longer make use of the foreign temples which had been established among them, but would worship their own old ancestral Gods alone. Then their whole youth took arms, and striking the air with their spears, marched to the Calyndic frontier, declaring that they were driving out the foreign Gods."
Plato in his Laws advocates that the state should punish those who deny the existence of the Olympian Gods or believe that the Gods exist but think they are indifferent to mankind or can be easily bought by bribes.
Interpretatio graeca the common tendency of ancient Greek writers to identify foreign divinities with members of their own pantheon, can be seen as a kind of exclusivism. The Syncretism of the Hellenistic period whereby aspects of the cults of foreign Gods such as iconography and epithets, can also be seen as a kind of exclusivism.