Some cases related to the fight against terrorism, among others, have challenged some of the categories of international law on the use of force, generating a constant confrontation between what is considered legitimate and what is legal. The invasion of allied countries in Iraq and Afghanistan, the NATO intervention in Kosovo and the incursion of the Colombian state into Ecuadorian territory to attack a FARC guerrilla camp have put the existing legal regime to the test and highlighted some of its limitations, questioning the treatment given to concepts such as "legitimate defense," "armed attack," "necessity," and "proportionality." There are alternatives to overcome some of the main problems, including the possibility of revising the composition and decision-making procedure within the UN Security Council. The doctrine of the use of preventive force, which has been resorted to to a greater extent by states in the fight against terrorism, is a dangerous path that threatens to undermine rights and infringe on freedoms. Historically generally rejected, it is not advisable for the doctrine to be strengthened as an institution of public international law.