Complex sentence: In Germany, he reorganized the Shevchenko Scientific Society as an emigre institution and was it's Secretary General from 1947 to 1963, and, from 1952, President of its European branch.
Split into simpler sentences: In Germany, he reorganized the Shevchenko Scientific Society as an emigre institution. He was it's Secretary General from 1947 to 1963, and, from 1952, President of its European branch.