Complex sentence: When IRA members were interned at the outbreak of World War II, he went on the run, but was although he was arrested in 1940, and interned at the Curragh for the duration of The Emergency.
Split into simpler sentences: When IRA members were interned at the outbreak of World War II, he went on the run. He was eventually arrested in 1940 and interned at the Curragh for the duration of The Emergency.