At the beginning of the invasion, it is clear that the Persians held most advantages.[183] Regardless of its actual size, it is clear that the Persians had brought an overwhelming number of troops and ships to Greece.[30][184] The Persians had a unified command system, and everyone was answerable to the king.[185] They had a hugely efficient bureaucracy, which allowed them to undertake remarkable feats of planning.[22][186][187] The Persian generals had significant experience of warfare over the 80 years in which the Persian empire had been established.[188] Furthermore, the Persians excelled in the use of intelligence and diplomacy in warfare, as shown by their (nearly successful) attempts to divide-and-conquer the Greeks.[189][190][191] The Greeks, by comparison, were fragmented, with only 30 or so city-states actively opposing the Persian invasion; even those were prone to quarrel with each other.[192] They had little experience of large-scale warfare, being largely restricted to small-scale local warfare,[193] and their commanders were chosen primarily on the basis of the political and social standing, rather than because of any experience or expertise.[194] As Lazenby therefore asks: "So why did the Persians fail?"[183]