求用英语翻译“修筑长城最初是为了抵御北方游牧民族(nomadic groups)的入侵.”

问题描述:

求用英语翻译“修筑长城最初是为了抵御北方游牧民族(nomadic groups)的入侵.”

At first, the Great Wall was built to defend against the attack by the northern nomadic tribes.