Complex sentence: Utterly defeated by Shaka's new Zulu Kingdom in the 1820s, the Makololo under the guide of Sebetwane were forced to march north until they conquered the Lozi and became the aristocracy of Barotseland, with Sebitwane as new "Litunga".
Split into simpler sentences: Utterly defeated by Shaka's new Zulu Kingdom in the 1820s, the remnant of the Makololo, under the leadership of Sebetwane, were forced to march northwards to escape. They conquered the Lozi and became the aristocracy of Barotseland, with Sebitwane as new "Litunga".