Once member of the First Triumvirate, and husband to Julius Caesar's daughter Julia, Pompey decided to ally with the Senate to oppose Caesar, leading to civil war. Pompey was ultimately defeated and the rebellion quelled, but Julius Caesar was still assassinated by senators loyal to the Republic.

Octavian, Julius Caesar's adopted nephew, would become Caesar Augustus. Under his leadership, he sought to make imperator an office and a title, effectively rendering the senate impotent and changing the republic into an empire. While all of the people mentioned in the answer options were involved in the assassination, only Octavian became imperator.

Roman military success was driven by the organization of the military. Organized into legions, Roman soldiers fought primarily as heavy infantry, were highly disciplined, and were able to fight effectively through a variety of terrain using tactically flexible formations.

Sparta was a society based around rigid military life. All young people trained to be in the army and as a result they were one of the strongest armies of the age. While Athens, Thebes, Argos, and Cyprus were all major players in Ancient Greece, Sparta is widely accepted as the most militant.

When Alexander the Great emerged victorious at the Battle of Gaugamela, the Persian emperor Darius fled the field and was slain by a bodyguard soon after.

Alexander the Great never invaded China, and Pu-Yi was an emperor who lived in the 20th century, long after Alexander's reign. 

Persian culture survived Alexander's invasion, and was even adopted by Alexander himself.

After Persia, Alexander continued through Asia; going as far as modern day Pakistan.

The Hellenic League's support of Alexander remained strong until his invasion of the Indian subcontinent.

The Mandate of Heaven justified the divine right of emperors to rule, but it also required certain responsibilities. If a sovereign did not fulfill his obligations, he could be overthrown.

The Divine Right of Kings was a concept from Europe that justified a hereditary ruler's right to rule; it made no allowances for rebellion or revolution and it stressed no responsibilities on the part of the sovereign.

The Social Contract is a concept originating in the European Enlightenment that explores the legitimacy of a government's authority of its people.

Noblesse Oblige was a concept that required noble leaders to take on leadership roles in their community.

The Gospel of Wealth is an idea first espoused by the industrialist Andrew Carnegie extolling the virtues of philanthropy as a means of responsible, top-down redistribution.

The Punic Wars were conflicts between Rome and Carthage. Carthage and its exceedingly powerful navy were expanding their empire to the east, as Rome secured the Italian peninsula and began greater expansion via land. In the second Punic War, Hannibal lead the Carthagian army over the alps to confront the Roman forces.

The Warring States Period led to the Establishment of the Qin Dynasty.

Mark Antony was Julius Caesar's political protege, Cleopatra was his ally and lover, and Octavian was his lieutenant and cousin.

Aristotle, Phillip of Macedon, and Alexander the Great all lived centuries earlier than Caesar.

Marcus Aurelius was an emperor who lived during the Pax Romana and is considered one of the most beneficent emperors in human history because he fought few wars, did not expand the empire at the cost of millions of lives, and attempted to outlaw gladiatorial fights to the death; he is also well studied because his personal diary, "The Meditations" is largely intact, and he has been portrayed by various actors in major Hollywood movies. Commodus was his son.

Spartacus was a slave who led a revolt against Rome and was only defeated when his army attempted to fight a pitched battle, a kind of fight the Romans excelled at.

Trajan and Hadrian were other famous emperors of Rome. Trajan is often considered a beneficent emperor who oversaw rising living standards, fought few wars, and did not expand the empire's borders at the cost of millions of lives. Hadrian is famous for building a large wall in England to attempt to stop invasions of Britons who did not submit to Roman authority.

At the battle of Cynoscephalae, Rome's army defeated a Macedonian force by using war elephants.

The Roman army never used firearms nor observation balloons.

The Roman maniples did use throwing spears, called pilum, that were designed to break after initial contact so they couldn't be thrown back at the Romans.