"In 1901, an Austrian doctor named Karl Landsteiner recognized the three basic blood groups – blood was first cross matched in 1907. Blood storage was still a problem during the early days of blood transfusion – while the compatibility issues had been resolved, blood still had a tendency to clot during storage.
Anticoagulants like sodium citrate were developed in the year 1914, allowing blood storage for an extended period of time. The discovery of Rh factor in 1940 allowed doctors to completely understand the compatibility issues among blood donors and recipients, and the American government started its first national blood collection program shortly thereafter."
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