In one sense the Magna Carta was an attempt to restrain the powerful nobles of the period who were bringing ruin on the countryside through war and high-handed behavior. “First drafted by the Archbishop of Canterbury to make peace between the unpopular King and a group of rebel barons, it promised the protection of church rights, protection for the barons from illegal imprisonment, access to swift justice, and limitations on feudal payments to the Crown, to be implemented through a council of 25 barons.
As an instrument it didn’t work, at least not until history had found a winner. “Neither side stood behind their commitments, and the charter was annulled by Pope Innocent III, leading to the First Barons’ War.” But after the English Civil War the Charter was resurrected as political myth and many of its ideas became incorporated into the US Constitution, the most important of which are that the most basic laws are restraints upon the powerful in order to keep them out of mischief.
More recently the tragic experience of the First and Second World Wars renewed interest in the concept of restraining nations through international law in order to avoid such mischief again. The huge human cost of 20th century conflicts made it apparent that world leaders were apt to get themselves into trouble unless they were bound to a certain code of behavior. To a certain extent “international law”, like the Magna Carta, is more of a political myth then enforceable statute, but it sort of, kind of worked for as long as the international system’s most powerful members clamped down on the misbehaving countries within the international system.
International law has emerged from an effort to deal with conflict among states, since rules provide order and help to mitigate destructive conflict. It is developed in a number of ways. …
Perhaps the first question to ask is whether in fact international law is law at all. The primary distinction between domestic and international law is that the latter often lacks an enforcement mechanism. There is no government to enforce the law, as there is in domestic situations. ….
Despite all of this, international law is often followed. This can be attributed in part to Great Power backing, but also much of international law is based on customary practice. International law may be enforced by states taking unilateral action if it is in their interest or through multilateral measures where sufficient consensus exists. Reciprocity can play a role, as benefits in other areas may be gained from following laws. In addition to ad hoc efforts to enforce international laws, a number of formal courts have been established for that purpose.