《资治通鉴·汉纪·汉纪三十三》
过去周朝把爵位分成五等，诸侯各自为政。衰微以后，枝叶强大，所以到了末期出现合纵连横的事，是形势发展的必然结果。
昔周爵五等，诸侯从政，本根既微，枝叶强大，故其末流有从横之事，势数然也。
In the past, Zhou Dynasty divided the titles into five levels, princes governed themselves. After the decline, branches grew strong. So in the later period, there were Alliance and Counter-Alliance. It was the inevitable result of the situation.