Simplify the following text for a Grade 9 native English-speaking person.
Original: After 1866 - when Venice and the Veneto region were united to Italy - in all Istria there was full support for the irredentism : Tino Gavardo , Pio Riego Gambini and Nazario Sauro where the most renowned between those who promoted the Istrian unification to Italy .
Simplified: After 1866 - when Venice and the Veneto region were united to Italy - in all Istria there was full support for the irredentism .