How about this for a start: Sometime after the accession of Emperor Shengzong to the throne of the Khitan Liao, the Song Dynasty manage to defeat the armies of Dowager Empress Xiao. The equivalent of the Treaty of Shanyuan is instead signed with the Song Dynasty getting the Sixteen Prefectures. Without the revanchists demanding a return of the Sixteen Prefecture, and without the constant military threat of the Khitans, the Song can spend less money on the military and more on internal stuff, such as industrializing.
Of course, this is only the political aspect.