Through diplomatic protection, aliens could invest abroad with the expectation that if they were injured in an unstable country, international law would provide an additional framework of protection. The US practice ensured that the content and scope of international obligations would extend beyond ad hoc diplomacy to international arbitration, where professional lawyers began to articulate general principles of state responsibility. The most important of these principles was the minimum standard of care owed to aliens. If a state failed to meet international standards, its legal responsibility was engaged. Latin American lawyers, however, were unhappy with state responsibility being applied in this way. In response to what they viewed as legal imperialism, Latin Americans expanded the doctrine to apply to the US and Latin Americans alike and to the violation of any international obligation and not just alien protection. In this way, what began as a narrow practice in Latin America, grew into a general framework of international law enforcement.

The Mexican Revolution is commonly perceived to have been the first social revolution. The revolutionary Mexican Constitution of 1917, at the time perhaps the most radical the world had seen, is well known, as is the subsequent oil nationalisation of the 1930s that it facilitated. Another significant, albeit less immediately striking, consequence of the revolutionary events that took place in Mexico between 1910 and 1920 was that a large number of claims were made against the Mexican state in respect of injuries caused to foreign nationals as a result of the revolution. Such claims found their basis in a (hotly contested) body of international legal rules that had emerged during the second half of the nineteenth century and first decades of the twentieth concerning alien protection: that is, concerning the rights of states to protect their nationals overseas and the duties of states when it came to the treatment of foreign nationals in their territory.2 The law of alien protection was also known as, or incorporated, state responsibility for injuries to aliens and diplomatic protection. Subsequently, six mixed claims commissions – with the United States, France, Germany, Spain, Britain and Italy – were set up to adjudicate Mexico’s international responsibility for claims that had arisen in respect of loss or damage caused by ‘revolutionary acts’ between 20 November 1910 and 31 May 1920.3 Loss or damage here encompassed personal injury, property loss or damage and breach of contract.4 Claims could be brought by ‘corporations, companies, associations, partnerships or individuals’.5 In addition, there was a second US commission, the ‘general commission’ (in contrast to the ‘special commission’, as the other US commission was known), which also had jurisdiction over certain other ‘revolutionary damage’ claims.6