It remained a weak concept, for its most important principle, established by the Treaty of Westphalia in 1648, was that of the sovereignty of states, which left each in effect unfettered by anything but judgement of self-interest. The only area over which states had agreed to limit the operation of self-interest lay not on land but at sea, which the leading powers had agreed at Paris in 1856 should be one where neutrality was respected and private military activity outlawed.
