Chua's thesis discussed throughout "Day of Empire" is that every hyper power of the world in history was tolerant by at least standards of its own time period. Every society that could be argued as reaching global hegemony was pluralistic during its rise to preeminence. Though the decline of an empire has coincided with intolerance, hatred of foreigners, and call of purity of race, religion, or ethnicity. However, it was tolerance that scattered the seeds of decline. Eventually tolerance reached its tipping point of conflict and violence. Chua considers a nation or empire a world-dominant power only if it meets three conditions. Power must definitely surpass the power of all known rival nations or empires. It also must not clearly inferior in economic or military strength to any other power in the world. Lastly, it must spread its power over such an immense area and population that it destroys the bounds of regional superiority.
The Achaemenid Empire starts with Cyrus the Great. In 550 BCE, he took over the Median kingdom and in 539, conquered the Lydian kingdom. Now the ruler of the largest empire that ever existed, Cyrus inferred little with the daily lives of his people, allowing them to keep their own gods and cultures, an example of his tolerance. Surprisingly, Cyrus tolerated religion by honoring temples, cults, and local gods of those he conquered. Darius the Great expanded Persian dominion into India, strengthened foothold in Greece, and made forays in eastern Europe. Near the outset of his reign, he contended with rebellions brought by his questionable nature of ascent to the throne. Darius took pride in the diversity of his empire, his cultural tolerance. He has respect for his empire's multilingualism and didn't impose Persian gods on his subjects. Darius even left local social structures intact but enforced local laws. Achaemenid Persia was a hierarchy and the kings ruled over an empire of unprecedented territorial scale, and policies of tolerance, making it possible for them to do so. The Achaemenids minimized the likelihood of opposition and revolt among conquered peoples by embracing local laws and traditions, allowing local languages, religions, and rituals to flourish. Xerxes, son of Darius, was very cruel and intolerant. However, he managed to preserve the Persian Empire. He raised the largest army on earth with his ability to incorporate men from every part of his empire. By 324 BCE, world dominance passed to the Greeks from the Persians. Alexander was the ruler of the largest empire in the history of Greece or Macedonia history. With Alexander's death, the empire immediately broke apart into warring kingdoms torn by internal rebellions.
Socially, Persians adopted customs like laws, cosmetics, manners, and architectural works. Specialized labor came with people with different skills working together to build buildings. Darius oversaw construction of new regional capitals and Persepoliz became an architectural wonder. Politically, there was tolerance of local leaders to capture kingdoms. For example, Cyrus respected local traditions and practices decreasing the likelihood of resistance and rebellion among those who were conquered. Economically, Darius introduced a standard currency and extended the empire's network of roads and communications system, including royal mail service, express messengers, and fire signals. He also formalized a system of imperial taxation and tribute.