The weakest aspect of the kingdom of the Seleucids was the internal fights in the dynasty. Repeatedly brothers, half-brothers, or their descendants faced eachother as rivals and rulers over different parts of the empire. They had the bad habit of giving cities and nobles royal land in return for their support if the disagreement continued for quite some time. This resulted in decreasing profits and central power for the royal house. Needless to say that this only increased the always present danger of separation in the heterogeneous empire.

Alexander the Great had started to urbanise especially the north-east corner of his empire with Greek and Macedonian colonists. This policy was continued by his successors. The area was in theory under the control of the Seleucid king, but it was situated so far away from the centre of the empire that he did not have much influence there. Around 250 the Greek rulers separated themselves from the Seleucid kingdom and they founded new kingdoms which covered Afghanistan, parts of Russian central Asia and western Pakistan. These kingdoms flourished from 235 till 185. The Greek culture took in a big place in these civilisations, and even in India were traces of the Greek culture found. This is not really surprising if you know that there had been regular political contact between the Seleucids and the Indian rulers.

The Parths.

Between this "far east" and the centre of the Seleucids a new empire was founded: the empire of the Parths. The Iranian tribe of the Parths was originally called Parni, and they had their roots in the area south and south-east of the Caspian sea. Around 250 they gained control over the adjacent satrap Parthia, and slowly their influence spread out over the whole Iranian highlands. In the course of the second century they also conquered Mesopotamia.

In the beginning their capitol was Ecbatana in Media, but later on it moved to Ctesiphon which was closely to Seleucia Tigris. They were ruled by the dynasty of Arsaciden who formed a feudal upper class. Their way of warfare was very different from the Hellenistic nations as they only used cavalry. The nobility formed groups of heavy armoured cavalry (cataphracten) while the people of the lower classes formed mounted archers. The Greek culture could continue its development under their leadership, and their kingdom even formed an asylum for Greeks who fled for the advancing Roman empire.

Further separations.

In the north-west and west of the Seleucid kingdom there were also constant separation movements. In Asia Minor the already mentioned kingdom of Pergamum and the tribalism of the Galatians were founded. Furthermore several small independent areas were already founded in the time of the diadochs: Bithynia with its mostly Thracian inhabitants, Pontus with kings who claimed to be descendants of the Persian dynasty of Achaemenidics, and Cappadocia which was a puny feudal nation with an Iranian upper class. Other separations of later date are Commagene in north Syria and Ituraea with its religious centre Heliopolis. The most important separation for the course of history was the founding of an independent Jewish nation of the Maccabaens or Hasmonaens.