Constitutional movement in Iran. The outcome of the Balkan Wars caused Russian and Britain to accept the probability of war with the Central Powers in the near future, suggesting the necessity of strong Anglo-Russian relations. Sazonov grew frustrated with Britain's inability to compromise on a route incorporating India, and threatened to proceed with the northern route. Fearing the implications of the impending war, Grey at last found it in Britain's best interest to concede at last, and agreed to initiate application of the railway under the Balmoral conditions. By this time Britain already had further consolidated its control over the Persian Gulf. By June 1914 surveys for the Enzeli-Tehran section had begun, and by 1915 the results of the Astara-Tehran part of the railway were completed and published. Still, progress on the railway was slow. Then, a few days after the outbreak of World War I, Russia repudiated its obligation to build the Tehran-Khanaqin line under the Potsdam Agreement. After World War I After the substantial interruption of World War I, the project for constructing a standard-gauge railway across Iran was initiated by Reza Shah Pahlavi as part of numerous reforms contributing to the drastic modernization of Iran that occurred over the two decades between World War I and World War II. Although technically independent, Iran was still a financially devastated and weak country. Yet the decade of the thirties brought the emergence of an economic market, a drastic increase in modern industries, a rise in exports, and an increase in agricultural output. Initially, British and Russian observers considered the implantation of railroads as the ultimate solution to the immense transportation problems Iran faced due to sparsely settled population, the lack of rivers, high mountains, and inhospitable desert regions of the country. Many Americans and British opposed the Trans-Iranian Railway, suggesting more efficient and less expensive modes of transportation, such as the U.S. Army's Motor Transport Service, which hauled about a fourth of the volume hauled by the railway to the Soviet border. Some British critics, including General Percy Sykes, opposed the railway because it ran north to south, rather than from west to east. The west to east route was preferred because it would allow the British direct access to their military bases in India and Mesopotamia, and at the same time, avoiding the threat of commercial loss of profit to Russia and any foreign rival. There were also