The Persian monarch was really, in his force, a petty prince compared to the Grecian republics, and therefore it behoved him, from views of safety more than from emulation, to interest himself in their quarrels, and to support the weaker side in every contest. This was the advice given by Alcibiades to Tissaphernes, and it prolonged near a century the date of the Persian empire; till the neglect of it for a moment, after the first appearance of the aspiring genius of Philip, brought that lofty and frail edifice to the ground with a rapidity of which there are few instances in the history of mankind. The successors of Alexander showed an infinite jealousy of the balance of power, a jealousy founded on true politics and prudence, and which preserved distinct for several ages the partitions made after the death of that famous conqueror. The fortune and ambition of Antigonus threatened them anew with a universal monarchy, but their combination and their victory at Ipsus saved them; and in after times we find that as the Eastern princes considered the Greeks and Macedonians as the only real military force with whom they had any intercourse, they kept always a watchful eye over that part of the world. The Ptolemies, in particular, supported first Aratus and the Achæans, and then Cleomenes King of Sparta, from no other view than as a counterbalance to the Macedonian monarchs; for this is the account which Polybius gives of the Egyptian politics. The reason why it is supposed that the ancients were entirely ignorant of the balance of power seems to be drawn from the Roman history more than the Grecian, and as the transactions of the former are generally the most familiar to us, we have thence formed all our conclusions. It must be owned that the Romans never met with any such general combination or confederacy against them as might naturally be expected from their rapid conquests and declared ambition, but were allowed peaceably to subdue their neighbours, one after another, till they extended their dominion over the whole known world. Not to mention the fabulous history of their Italic wars, there was, upon Hannibal’s invasion of the Roman state, a very remarkable crisis which ought to have called up the attention of all civilized nations. It appeared afterwards (nor was it difficult to be observed at the time​[22]) that this was a contest for universal empire, and yet no prince or state seems to have been in the least alarmed about the event or issue of the quarrel. Philip of Macedon remained neuter till he saw the victories of Hannibal, and then most imprudently formed an alliance with the conqueror, upon terms still more imprudent. He stipulated that he was to assist the Carthaginian state in their conquest of Italy, after which they engaged to send over forces into Greece, to assist him in subduing the Grecian commonwealths.