Illegally crossing borders is a kind of international criminal activity. There underlie complicated causes for it, including geographical and historical factors, labor force market, economic interests, foreign immigration policy and so on.

• 非法出入境是一种跨国性质的违法犯罪活动,它的成因比较复杂,有地缘及历史原因,也有劳动力市场、经济利益、外国移民政策等方面的原因。