What is the main idea of "the heavenly horses of Han Wudi

The Emperor Wu of Han received reports of the tall and powerful horses ("heavenly horses") in the possession of the Dayuan, which were of capital importance to fight the nomad Xiongnu. The refusal of the Dayuan to offer them enough horses along with a series of conflicts and mutual disrespect resulted in the death of the Chinese ambassador and the confiscation of the gold sent as payment for the horses.