Complex sentence: In even years seminars are held in USA, in the uneven years the seminars are held outside the USA and are often jointly organized with similar organizations and institutes such as the French Association of Pyrotechnic.
Split into simpler sentences: In even years, seminars are held in USA and in the uneven years, the seminars are held outside the USA. Meetings are sometimes jointly organized with similar organizations and institutes such as the French Association of Pyrotechnic.