See, this is why we really need, for social science questions like these, to actually define and be specific in what we're asking. There are many ways you can judge what it means to being the longest successful civilization, since it could be dynasty specific or just a general overall country/population as a whole. And don't get me started on how we could possibly demarcate successful in this question. China went through many dynasty changes, but the civilization itself didn't end by any means. Technical questions are always better imo imo >.>