Emperor Yang conscripts over a million men in spring 608 to construct the Yongji Canal, from the Yellow River to Zhuo Prefecture (roughly modern Beijing).

It is said that there were not enough men, and that he started conscripting women as well.

The Western Tujue khan (Ashina Rangan's western rival), the Heshana Khan Ashina Daman, whose mother was Han, submits to Sui as a vassal in 608 after persuasion by the Sui official Cui Junsu However, in the same year Emperor Yang receives a letter claiming to be from the King of Japan, Duolisibigu (now commonly believed to be Prince Shōtoku), stating, "The Son of Heaven where the sun rises, to the Son of Heaven where the son sets, may good health be with you."

Displeased by what he sees as insolence, he orders that in the future, "insolent" letters from other states not be submitted to him.

Also in 608, Emperor Yang's relationship with Yang Jian begins to deteriorate, initially over disputes over women (Yang Jian's having taken a concubine that Emperor Yang himself wanted) and hunting (Yang Jian's guards having been much more successful than Emperor Yang's guards at hunting).

He ordered investigations into Yang Jian's violation of laws, and discovers that Yang Jian had used witchcraft to curse Yang Zhao's three sons.

In anger, Emperor Yang executes and exiles a number of Yang Jian's associates, but he does not depose Yang Jian, although from this point on Yang Jian does not exert much influence on the political scene.

In 608 also, Pei Ju persuades the Tiele tribes to attack Tuyuhun, forcing Tuyuhun's Busabuo Khan Murong Fuyun to flee.

Murong Fuyun initially considers submitting to Sui, and Emperor Yang sends Yuwen with an army to welcome him.

However, when Murong Fuyun changes his mind, Yuwen attacks him and seizes much of Tuyuhun's populace.

When Murong Fuyun flees further, Emperor Yang has his forces seize Tuyuhun's territory, establishing four prefectures, to be populated with exiles.

The Persians reach the Bosporus by 608, laying siege to Chalcedon.

The Western Turks, having lost the first war against Persia thirty years earlier, seek to change their fortunes while Persia is engaged fighting the Eastern Roman (Byzantine) Empire.

They invade eastern Persia with a large number of men, but are defeated in the first battle near the fort of Tus in Khorasan by a force of two thousand Savaran (elite heavy cavalry).

Having lost this battle, the Turks and Hephthalites request reinforcements from the Khagan.

Sebeos exaggerates that three hundred thousand troops were sent to reinforce the invading army.

This force soon overruns Khorasan, as well as the fort of Tus, with its three hundred defenders under prince Datoyan.

However, the Turks withdraw after their raids, which go as far as Isfahan.

Smbat IV Bagratuni quickly reorganizes the eastern Persian forces and finally crushes the Turks and Hephthalites, reportedly killing their leader in hand-to-hand combat.

After the death of their leader, which shatters troop morale, the Turks and Hephthalites retreat in a disorderly manner.

The Savaran pursue them, killing many.

Ashina Rangan makes another visit to Emperor Yang in spring 609, and the emperor again rewards him with much treasure.

At the same time, Emperor Yang orders the redistribution of the farming land throughout the empire.

Also in 609, Emperor Yang, jealous of the literary talent of the official Xue Daoheng, falsely accuses Xue of defaming the emperor and has him strangled.

By this time, it is said that Emperor Yang's lifestyle has become particularly wasteful, and that he no longer feels bound by moral principles.

The emperor conducts a tour of the newly conquered Tuyuhun territory later in the spring, and sends several generals to chase down Murong Fuyun.

The Sui forces engage Murong Fuyun's remaining forces, with mixed success, but Murong Fuyun is forced to flee to Dangxiang tribes.

Emperor Yang tries to impose Murong Fuyun's son Murong Shun, whom Murong Fuyun had earlier sent to Sui as a hostage, as Tuyuhun's new khan, but the Tuyuhun people will not accept him, and Murong Shun is forced back to Sui territory.

Emperor Yang also receives twenty-seven rulers of Xiyu (Western Regions) kingdoms in an audience at Zhangye (in modern Zhangye, Gansu).

Ashina Rangan, khagan of the Easturn Turks, dies in late 609 and is succeeded by his son Shibi Khan Ashina Duojishi.

Pursuant to Tujue customs, Ashina Duojishi requests permission from Emperor Yang of Sui to marry Ashina Rangan's wife Princess Yicheng (the daughter of a clansman of Emperor Yang).

Emperor Yang agrees.

The fate of the deposed Lakhmid king Al-Nu'man III ibn al-Mundhir after his arrival at Ctesiphon is largely disputed, even in near-contemporary sources; he was either immediately executed or imprisoned for a period of time and then executed, but in 609 he is certainly dead and his former friend Iyas ibn Qabisah al-Ta'i, an Arab of the tribe of Tayy, has been installed, marking the end of the dynasty, although Nu'man's son al-Mundhir will try to revive the kingdom during the Ridda wars (632-33) and will rule the Bahrain region for a short period of eight months until he is captured.

At an indeterminate date, an open clash between the Persians and their Arab auxiliaries, on one hand, and Arab tribesmen, on the other, occurs at Dhi Qar.

According to certain Muslim traditions, the battle took place in the year 623 or 624.

Modern scholars have narrowed this range to 604-11.

Arab sources number the Persian force at two thousand soldiers, with three thousand Arabs led by Iyas ibn Qabisah.

The Arab force opposing the Persians, with their Arab auxiliaries, is from the Bakr ibn Wa'il, a large tribal confederation whose territory extends from southwestern Iraq into the eastern Arabian peninsula.

The most prominent constituent tribe is the Banu Shayban, the other groups being the Banu 'Ijl, Banū Zohl, Banu Qays ben Thalaba, Banu Taym Allah ben Thalaba, and Banu Yashkor.

These groups do not seem to have coordinated their efforts on the battlefield, nor did they have a single commander in chief.

Rather, leadership seems to have shifted among various warriors.

Nevertheless, the Banu Bakr defeat the combined Persian and Arab forces.

Some scholars, apparently influenced by the Muslim tradition, have interpreted the battle of Dhi Qar as part of a prolonged Arab rebellion against the Persians, which culminated in the Muslim conquest of the Persian empire.

As Shaybani tribesmen, led by Mosannā ben Haresa, assisted in the conquest of Iraq, it has been argued that the Bakr, and especially the Shayban, had followed a distinct anti-Sasanian policy since Dhi Qar.

Scholars have shown, however, that the Shayban who supported the Muslims and those who were prominent at Dhi Qar belonged to different, even rival clans; some Shaybani leaders allied themselves with the Persians after Dhi Qar, and others even opposed the Muslims during the conquest of Iraq.

The battle of Dhi Qar thus appears to have had ideological and symbolic meaning for the Arabs far beyond its military and political significance.

Emperor Yang visits Jiangdu again in 610, and this time elevates Jiangdu's importance so that it effectively becomes a third capital.