My parents went to Venice on holiday a few times in the 1970s. No, it was not overburdened with tourists. I have seen many photos and heard good stories. The insane levels seen in Venice and Amsterdam only started in the last 10 years.

I don't think that's coincidence. Cheap air travel opened a window on the world and absolutely ruined a lot of places. To the point that if you haven't visited Machu Picchu the consensus is that you haven't really lived. Tourists are roaches, they bring some much needed income to some places but they utterly ruin others, crowd out the locals, cause living spaces to be converted into hotels and make it impossible to buy food and drink at normal prices for the people that live there.

And also provide a considerable to major contribution to the GDP of affected countries. We like it or not it is an export.