This retreat was only a postponement. During the next decade Japan set up a strategic shield to the east and south by fortifying the mandated islands of the Pacific, awarded to her after the war. Treaties and agreements were violated whenever convenient, and in 1931 she turned westward again to satisfy her appetite for Russian and Chinese territory. The time was well chosen. With the Western nations in the depths of an industrial depression, Japan began a series of aggressions against the Chinese in Manchuria. The gains were consolidated in a puppet state known as Manchukuo, comprising a fertile and populous area as large as California. China was unable to offer much resistance, and Soviet Russia could not risk a major war in the Far East. Even so, some of the Soviet border clashes with the Japanese in time of “peace” were actually battles fought with tanks and planes. In 1937 came the Japanese invasion of China proper. Germany and Italy were launching aggressions of the same stamp in Europe and Africa, and the world was to know little stability until all three totalitarian states had been crushed in World War II. Soviet Russia had a grim struggle for survival while resisting the full tide of Nazi invasion. But at the time of the Yalta Conference, Stalin was in a position to ask a stiff price for military aid in the Pacific. The United States agreed that the Port Arthur area and southern Sakhalin should be returned to Russia to redress the “wrongs” of 1905. Concessions were also made in Manchuria and outer Mongolia. Stalin, for his part, consented to sign a treaty of friendship with Nationalist China as an ally of the United States. Later events made it evident that he had no intention of keeping his pledges. On the contrary, Soviet policy already visioned a Communist empire in the Far East which would include China as well as Korea. The Yalta Agreement was stridently criticized in the United States after Stalin’s duplicity became apparent. But the War Department took a realistic view as early as the spring of 1945: “The concessions to Russia on Far Eastern matters which were made at Yalta are generally matters which are within the military power of Russia to obtain regardless of United States military action short of war.... The Russians can, if they choose, await the time when United States efforts will have practically completed the destruction of Japanese military power and can then seize the objectives they desire at a cost to them relatively much less than would be occasioned by their entry into the war at an early date.”[4] [4] U. S. War Dept memo for Acting Sec of State, 21 May 45, quoted in Joseph C. Grew, _Turbulent Era: A Diplomatic Record of Forty Years_ (Boston: Houghton Mifflin, 1952), 2:1457–1458.