Complex sentence: However, the Yenisei Kirghiz spent much of their time in a state of rebellion, and in 840 they succeeded in sacking the Uyghur capital Ordu-Baliq in Mongolia's Orkhon valley, and driving the Uyghurs out of Mongolia entirely.
Split into simpler sentences: However, the Yenisei Kirghiz spent much of their time in a state of rebellion. In 840 they succeeded in sacking the Uyghur capital, Ordu-Baliq in Mongolia's Orkhon valley, and driving the Uyghurs out of Mongolia entirely.