Complex sentence: The performance of this operetta was cancelled in London because the beginning of the World War I. After that, he left London for the United States and during his stay in New York he became very ill. He died at the age of 38.
Split into simpler sentences: The performance of this operetta was cancelled in London because the beginning of the World War I. Therefore he left London for the United States. During his stay in New York he became very ill. He died at the age of 38.