So long as they were resolute to maintain their footing on the right bank of the Euphrates, in Phrygia, Cappadocia, and upper Syria, they were of necessity mixed up with the quarrels of the west.

Could they have been content to withdraw within the Euphrates, they might have remained for the most part clear of such entanglements; but even then there would have been occasions when they must have taken the field in self-defence.

As it was, however, the idea of abstention seems never to have occurred to them.

It was the fond dream of each "Successor" of Alexander that in his person might, perhaps, be one day united all the territories of the great Conqueror.
Seleucus would have felt that he sacrificed his most cherished hopes if he had allowed the west to go its own way, and had contented himself with consolidating a great power in the regions east of the Euphrates.
And the policy of the founder of the house was followed by his successors.

The three Seleucid sovereigns who reigned prior to the Parthian revolt were, one and all, engaged in frequent, if not continual, wars with the monarchs of Egypt and Asia Minor.