Irregular mass migration is among the “hybrid threats” that rivals can use to undermine the stability of NATO countries, the alliance recognised in its new strategic concept agreed on Wednesday in Madrid. The inclusion of such threats was an explicit request from countries on NATO’s outer rims, including the summit’s host Spain, whose neighbours have been accused of using migration as a weapon of political pressure. Poland’s border crisis with Belarus last year was another example. The strategic concept twice mentions migration as an element to monitor in the next decade, and points to the sou…