Complex sentence: Fortunately for Znaniecki he was a visiting professor at Columbia University in 1939 at the outbreak of World War II. Thus he was spared the tragic history of his motherland at that time (3).
Split into simpler sentences: Fortunately for Znaniecki, at the outbreak of World War II, he was a visiting professor at Columbia University. Thus, he was spared the tragic history of his motherland (3).