The use of military forces by democratic States in the fight against globalized criminal threats (terrorism, illegal trade in drugs, arms, intellectual property,...) is viable and necessary. However, it is important to know when and how military forces may be used legitimately. To do so, it is necessary to understand the transformation of the threat - armed groups, which once challenged governments over ideology, now seek financial gain for themselves. While allegedly espousing ideological politics at both ends of the political spectrum (extreme left and right), these groups have created sinister alliances that ignore geographic and political boundaries. This transformation challenges State security and puts the institutional structures of democratic States at risk. Military forces must develop an understanding of the law that will apply when combating these criminal/terrorist groups. That law will come from human rights law and international humanitarian law. The determination of when each will apply presents new challenges for military forces that have traditionally focused on the law applicable to international armed conflict. This article will explore these issues from a Colombian perspective, a country which has been engaged for decades in an armed struggle with insurgent groups and now also with criminal groups using terrorist tactics for economic gain through the drug trade.