While much of Europe experienced hunger and hunger-related deaths during the era of the First World War, famine, as defined by an excess mortality rate of 40 per thousand, occurred mainly in the Russian Empire and later Soviet Russia. Furthermore, famine continued in Russia through 1922. In Russia there were two stages of the food problem. 1914–19 was characterized by mutual international blockades that upset regular international trade and caused general hunger with some elevated mortality. Patterns of supply were strained, especially in areas where mortality rose to famine levels. Leaders were slow to recognize the crisis, believing that excess grain production in other parts of the Empire would compensate for regions with reduced food supplies, which they did not. From 1919 to 1922, while trade had opened back up in much of Europe, it did not in Russia, which remained subject to blockade and to civil and international war. Hunger and famine in this period was much more severe, and US aid relief did not enter Soviet Russia until 1921, the final and most terrible year of the famine.