根据提供的一段中文文本，翻译成英文。


“公元前221年秦始皇统一中国，设立郡县制，把全国划分为36个郡，每个郡设丞相一人。”
"In 221 BC, Emperor Qin Shi Huang unified China and established a system of prefectures and counties, dividing the entire country into 36 prefectures with one prime minister appointed for each."