Complex sentence: The Czechoslovak state expressed an interest in the building but the Nazi occupation of Czechoslovakia on 15 March 1939 and establishment of the "Protectorate of Bohemia and Moravia" thwarted its plans.
Split into simpler sentences: The Czechoslovak state expressed an interest in the building. But the Nazi occupation of Czechoslovakia on 15 March 1939 and establishment of the "Protectorate of Bohemia and Moravia" thwarted its plans.