Complex sentence: It also marked the debuts of the Soviet Union and Northern Ireland, and it remains the only occasion on which Italy failed to qualify (Italy did not take part in the 1930 tournament but there was no qualification for that competition).
Split into simpler sentences: It also marked the debuts of the Soviet Union and Northern Ireland. The 1958 competition remains the only occasion on which Italy failed to qualify (Italy did not take part in the 1930 tournament but there was no qualification for that competition).