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.