The Romans had favored Demetrius, and Perseus' role in killing Demetrius has not endeared him to Rome.

As king, Perseus campaigns, as his father had done, to extend Macedonian power to the northeast and south, extending his influence in Thrace and Illyria.

One of his first acts on becoming king had been to renew the treaty with Rome.

However, he solicits alliances with the Achaean League and other Greek states, which some of the leaders hostile to Rome would like to accept, and makes special efforts to win over the Greek world.

To this end, …

Perseus resumes control of the Delphic Amphictyony, …

…establishes excellent relations with Rhodes, and …

…encourages revolution in Aetolia and …

…Thessaly.

The Middle East: 177–166 BCE

The Sixth Syrian War and the Ascendancy of Roman Influence

The era from 177 to 166 BCE is marked by the turbulent events of the Sixth Syrian War, a critical confrontation between the Seleucid Empire under Antiochus IV Epiphanes and Ptolemaic Egypt. The causes of this war are somewhat obscure, but the immediate provocation arises in 170 BCE when the two regents of Egypt's young king Ptolemy VI Philometor, Eulaeus and Lenaeus, declare war against the Seleucids.

Initially successful, Antiochus swiftly captures strategic positions, notably the fortress city of Pelusium. Realizing the disastrous course of their strategy, the Egyptians depose the original regents, replacing them with Comanus and Cineas, who seek peace negotiations. Antiochus exploits the turmoil by taking Ptolemy VI, his nephew, under his guardianship and effectively assumes control over Egypt. The people of Alexandria, however, reject this arrangement and proclaim Ptolemy VIII Physcon as the sole ruler.

Antiochus responds by besieging Alexandria, but unable to sever its supply lines, he withdraws by the end of 169 BCE. In his absence, reconciliation occurs between Ptolemy VI and his brother, undermining Antiochus' position and prompting a renewed Seleucid invasion. Facing imminent conquest, the Egyptians appeal to Rome, marking a critical turning point.

In 168 BCE, Roman envoy Gaius Popilius Laenas confronts Antiochus near Alexandria. In a dramatic scene at Eleusis, Popilius famously draws a circle around Antiochus, demanding a decision on the Roman Senate’s ultimatum—immediate withdrawal from Egypt and Cyprus. Antiochus, cornered by Rome's authority, concedes, marking the event remembered as the "Day of Eleusis," effectively ending Seleucid ambitions in Egypt.

This era also sees the continued consolidation of the Parthian kingdom under Phraates I, who expands Parthian control beyond the Gates of Alexander and captures strategic locations like Apamea Ragiana. The groundwork laid during his reign paves the way for the extensive territorial expansion that will soon be realized by his successor, Mithridates I.

Thus, the era 177–166 BCE signifies the waning of Seleucid power, the consolidation of Roman authority in Mediterranean geopolitics, and the rising prominence of Parthia, reshaping the geopolitical landscape of the Middle East significantly.

The causes of the Sixth Syrian War are obscure.

Eulaeus and Lenaeus, the two regents of the young king of Egypt, Ptolemy VI Philometor, declare war on the Seleucid ruler Antiochus IV Epiphanes in 170.

Ptolemy's younger siblings Ptolemy VIII Physcon and Cleopatra II are in the same year declared co-rulers in order to bolster the unity of Egypt.

Military operations do not begin until 169, when Antiochus quickly gains the upper hand, seizing the important strategic town of Pelusium.

The Egyptians realize their folly in starting the war, Eulaeus and Lenaeus are overthrown and replaced by two new regents, Comanus and Cineas, and envoys are sent to negotiate a peace treaty with Antiochus.

Antiochus takes Ptolemy VI (who is his nephew) under his guardianship, giving him effective control of Egypt.

However, this is unacceptable to the people of Alexandria, who respond by proclaiming Ptolemy Physcon as sole king.

Antiochus besieges Alexandria but he is unable to cut communications to the city so, at the end of 169, he withdraws his army.

In his absence, Ptolemy VI and his brother are reconciled.

Antiochus, angered at his loss of control over the king, invades again.

The Egyptians send to Rome asking for help and the Senate dispatches Gaius Popilius Laenas to Alexandria.

Meanwhile, Antiochus has seized Cyprus and Memphis and is marching on Alexandria.

At Eleusis, on the outskirts of the capital, he meets Popilius Laenas, with whom he had been friends during his stay in Rom, but instead of a friendly welcome, Popilius offers the king an ultimatum from the Senate: he must evacuate Egypt and Cyprus immediately.

Antiochus begs to have time to consider but Popilius draws a circle round him in the sand with his cane and tells him to decide before he steps outside it.

Antiochus chooses to obey the Roman ultimatum.

The "Day of Eleusis" ends the Sixth Syrian War and Antiochus' hopes of conquering Egyptian territory.

Phraates I is recorded as expanding Parthia's control past the Gates of Alexander and occupying Apamea Ragiana, the locations of which are unknown, yet the greatest expansion of Parthian power and territory takes place during the reign of his brother and successor Mithridates I of Parthia.

Relations between Parthia and Greco-Bactria deteriorate after the death of Diodotus II, when Mithridates' forces capture two eparchies of the latter kingdom, at this time under Eucratides I.

Brahmanism competes in the political and spiritual realm with Buddhism in the Gangetic plain.

Buddhist sources, such as the Asokavadana, mention that Pusyamitra was hostile towards Buddhists and allegedly persecuted the Buddhist faith.

A large number of Buddhist monasteries (viharas) were allegedly converted to Hindu temples, in such places as Nalanda, Bodhgaya, Sarnath or Mathura.

While it is established by secular sources that Hinduism and Buddhism were in competition during this time, with the Sungas preferring the former to the latter, historians such as Etienne Lamotte and Romila Thapar argue that Buddhist accounts of persecution of Buddhists by Sungas are largely exaggerated.

The traditional narratives are dated to two centuries after Pushyamitra’s death in Asokâvadâna and the Divyâvadâna, Buddhist books of legend.

The Asokavadana legend is likely a Buddhist version of Pusyamitra's attack on the Mauryas, reflecting the declining influence of Buddhism in the Sunga Imperial court.

Support of the Buddhist faith by the Sungas at some point is suggested by an epigraph on the gateway of Barhut, which mentions its erection "during the supremacy of the Sungas".

On the other hand, Sir John Marshall noted that the Sanchi stupa was vandalized during the second century BCE before it was rebuilt later on a larger scale, suggesting the possibility that the original brick stupa built by Ashoka was destroyed by Pusyamitra and then restored by his successor Agnimitra.

Similarly, the Deokothar Stupas (geographically located between Sanchi and Barhut) suffered destruction during the same period, also suggesting some kind of involvement of Sunga rule.

Proponents also point to the proclamations and claim that the Manu Smriti was propagated.

Under the Sunga dynasty, stupas—brick-faced, domical mounds containing the relics of the Buddha, whose form symbolically represents the Buddhist universe—will become increasingly elaborate structures.