Hindering communications of the Western powers in the 4th century BC.
The rulers of the Iranian highlands created one of the largest empires of the pre-Christian period but the nomadic tribes f the nor thindered their advance. The second limitation of their expansion happened in the West when, after their failed invasion of Scythia, their Ionians subjects revolted. The Ionians’ western relatives, from metropolitan Greece, were involved in the conflict thus forcing the Achaemenids to attempt another expansion which ended ingloriously by the end of the Persian Wars and cost them Cyprus and half of their Asia Minor province. They managed to recover their loses with their involvement in favor of the Lacedaemonians during the Peloponnesian War.
The next difficulty the Achaemenids faced was the effort of the Spartan king Agesilaus to solve the problem of the unemployed mercenaries of the Peloponnese war with the second attempt of the Greeks to invade Asia Minor. The solution was given by the Achaemenids, who thanks to their gold caused revolutions against her of Spartan hegemony, thus obstructing the communications of Agesilaus and forcing him to abandon his campaign. This solution was considered effective and that is why there would be an attempt to repeat it during the second Greek invasion from the West under Alexander the Great.
The Achaemenids considered the defeat at Granic only an accident but their next defeat at Issus showed them how serious the western threat was this time. The discovery of anti-Macedonian factions ambassadors in the occupied camp of Darius at Issus silenced most treasonous voices in Alexander;s rear but not all. But the Persian king had sent the satraps Pharnavazos and Autophradates with a fleet to either occupy the Aegean islands or even install pro-Persian governments with rich bribes. The purpose was to trap Alexander in Asia and to cause desertions in his army. This made Alexander to advance towards Phoenicia in order to cause similar concerns among the Phoenician crews of the Persian fleet. Arados, Byblos and Sidon surrendered but Tyre and Gaza they resisted. despite their fleets being absent in the Aegean. They relied on their strong defensive locations but they were captured and destroyed.
The Persian satraps in the Aegean may have had issues with their crews’ loyalty but they gave money to the Spartan king Agis III as well as the surviving from the battle of Issus, Greek mercenaries of Darius, about 8000 strong. Alexander which had conquered the homes of the Phoenician sailors and also Egypt (granary of the then known world), turned towards the interior of Asia considering that he actually had trapped the satraps who could no longer communicate with Darius or resupply. But they had managed to create enough problems and only the destruction of the Persian fleet by the Macedonian admiral Hegisilochus forced the satraps to submit to Alexander.
It wasn’t the end though. With the money and the former mercenaries of Darius o king Agis defeated the Macedonian garrison of Corinth and raised an anti-Macedonian revolution in the Peloponnese. The other Greeks, however, remained neutral and the Messenians did not want to become helots of Sparta again. The regent of Macedonia Antipater crushed the rebels at Megalopolis and Alexander unhindered overthrew the Persian empire. Although Alexander officially considered the episode with Agis III is unimportant, as the current situation shows that the successors of the Achaemenids have studied history very well.
Sources:
Xenophon «Hellenika» mtf. E. Shepherd (1793)
Xenophon «Agesilaos» mtf. E. Shepherd (1793)
Plutarch «Alexander» Loeb Classic Library edition 1920
Diodorus Siculus «Histories» Loeb Classic Library 1914 edition
Arrian «Alexandrou Anavasis», Loeb Classic Library edition 1914
Stefanos Skarmintzos 