Complex sentence: The outbreak of World War II on 1 September 1939 and the ensuing Phoney War had made it possible to predict a violation of Luxembourgish neutrality, so that the government decided it would depart into exile if the country was completely occupied by German forces.
Split into simpler sentences: The outbreak of World War II on 1 September 1939 and the ensuing Phoney War indicated that Luxembourg's neutrality would likely be violated. The government decided it would depart into exile if the country was completely occupied by German forces.