Just like the headline says - your challenge is to make and keep the Republic of Venice independent all the way to 2019.
The Republic doesn't need to control any territory outside the city of Venice itself to count for the challenge but the city itself must be independent (i.e, not part of a modern/unified Italy or not part of a Austrian Empire to name two examples) to count for the challenge.
The Republic doesn't need to control any territory outside the city of Venice itself to count for the challenge but the city itself must be independent (i.e, not part of a modern/unified Italy or not part of a Austrian Empire to name two examples) to count for the challenge.