Although the Greater Yuezhi and Northern Yuan lay in between, the Persians were naturally warlike. In the past, their inaction had to do with both Tenge and the instability within Northern Yuan.
Right now, Northern Yuan was at peace, and Xiao Qinian had completely seized supreme power while their army was expanding. For Persia, this was already an excellent pretext.
As for the Greater Yuezhi, Libo was on the rise. Whether he defeated Tenge or was wiped out by Tenge made no difference to Persia; it was merely a matter of what excuse they would use to make their move.
Chapter 626