Complex sentence: Tang paid compensation and promise further tributes, Illig Qaghan ordered to withdraw their iron cavalries (Alliance of Wei River, 渭水之盟 or Alliance of Bian Qiao 便橋會盟/便桥会盟).
Split into simpler sentences: Tang paid compensation and promised further tributes, so Illig Qaghan ordered to withdraw their iron cavalries. This is known as the Alliance of the Wei River, (渭水之盟) or the Alliance of Bian Qiao (便橋會盟/便桥会盟).