This is a topic that has fascinated me since I first read the Hunchback of Notre Dame and found the story was very much about the building as much as the people. The short answer is a social change occurred during the 17th century. The novel Victor Hugo wrote is a part of this. Though historic sites are still targeted during war often. Currently you can see the Taliban actively perusing this destruction in part to erase cultural icons they disagree with and to demoralize. The Nazis did this also. I mention this as it's easy to assume things are just in the past and we as modern people are better than our ancestors. We've not changed as people quite that much. Now for the longer answer.

In England some of the changes came with Railroads and the loss of common lands. A particular case that set a precidence was the Berkhamsted case. Lord Brownlow erected five foot steel fences claiming the town commons as private property. This was in 1866. For most of English history common land was a vital part of every town. People gathered, did trade, and celebrated together in this commons. This is where one gets a town square also. As the wealthy landowner began to take these away, with instances as far back as 1660 but with growing rapidity especially in the early Victorian Era this became representative of the divides of "Us" snd "Them".

What makes the Lord Brownlow and Berkhamsted case so interesting is the response of the people. Augustus John Smith lead a group of hired men from the East End and locals to tear these fences down in an effort to reclaim the public land and preserve it. This is known as the Battle of Berkhamsted Common. It wasn't until 1870 that laws were passed under the guidance of Sir Robert Hunter  and others who eventually confounded the Commons Preservation Society and National Trust.

Now if you're talking We as in the United States the history begins with the 1850 presentation of Hasbrouck House. This is also known as George Washington's military headquarters. In the US this was the first site designated as a historical site to be preserved. It was reaffirmed as a historic landmark site in 1961 under some changes to Legislation as well. It's currently a Museum that's replicating life as Washington experienced it. This lead to presentation of Mount Vernon in 1858. Various US States has their own Societies but I believe it was the Association for the Preservation of Virginia Antiquities that came first. This organization is now known as Preservation Virginia, to aide you in future research. This lead to the 1895 creation of the American Scenic and Historic Preservation Society. This was the first US Nationwide Preservation effort.

I don't know enough about other English speaking countries Preservation to say much about Australia or Canada. That said you can see none of this occured in a vaccume. We as a global people often influence one another.  This is why organizations like Unesco exist and matter.

Back to Hugo to wrap this up he existed during the aftermath of a war that used destruction of everything tied to wealth as a part of its driving force. Paris was destroyed. Things we cannot know were lost. His own parents were at odds theologically as his father was an atheist and his mother a catholic. His father took him with him as he worked as one of Napoleon's generals. Hugo essentially was raised on war and revolution and as he became a man saw the restoration of the Bourbon Monarchy. This shows in Les Miserables but it is also very present in Hunchback which was written not to tell us a story about people but about a building and the price of losing its art. You can compare this to his earlier work "Guerre aux Démolisseurs (War to the Demolishers)." As Hunchback is one of the most adapted and translated works it is possible that it's influence echoed the people's desire to remember and also inspired it.

For more on Hugo and the preservation movement: Zaretsky, Rob. "Victor Hugo and Architecture", Engines of our Ingenuity, 2006 radio transcript, University of Houston

Rebello, Stephen. The Art of The Hunchback of Notre Dame 

Notre-Dame De Paris at Project Gutenberg, 1888 English translation by Isabel Florence Hapgood

https://www.architectmagazine.com/design/editorial/victor-hugo-was-wrong_o

For people specific research besides Victor Hugo and those above you will find interest in the following people: Eugène Viollet-le-Duc - An architect who focused on restoration and the influences of the past on future design. They were instrumental in saving Notre Dame Cathedral and their works continue to influence art and architecture. As Notre Dame was one of the first reconstructive restorations this is to me one of the most important people to learn about. I am offering tidbits below but they're all fascinating people.

The designer William Morris who besides making Arsenic Wallpaper en vogue established the Society for the Protection of Ancient Buildings.

Harriet Tubman who bought 25 acres to make a home for the Elderly and has become a museum and memorial to her other great works.

Ann Pamela Cunningham was one of the main forces behind the saving of Mount Vernon via her formation of the Mount Vernon Ladies' Association. She was also disabled adding interest for me personally as navigating historical sites in a wheelchair is a challenge with the ADA. Imagine preservationists working without ability and across all 30 states?

Mary McLeod Bethune and Madame CJ Walker were both pivotal in preserving African American history. Madame Walker made the largest donation for the preservation of Fredrick Douglas' home while making history as the first female self made Millionaire in the USA. Bethune was a national advisor to FDR amid many more achievments.

Resources/ 3am Bibliography

Mr. Shaw-Lefevre on the Preservation of Commons". The Times. 11 December 1886.

Exhibition and commemorative walk marks anniversary of battle to save Berkhamsted Common". Hemel Gazette. Johnston Publishing Ltd. 12 October 2015

Denise Winterman. "The man who demolished Shakespeare's house". BBC News Magazine

"The National Trust Acts 1907 - 1971, as varied by a Parliamentary Scheme implemented by The Charities (National Trust) Order 2005"

Tribute to Enduring Ideals." A Richer Heritage: Historic Preservation in the Twenty-First Century.

Lindgren, James Michael. Preserving the Old Dominion: historic preservation and Virginia traditionalism. 

Murtagh, William J. Keeping Time: The History and Theory of Preservation in America. New York: Sterling Publishing, Co., 1997.

Restoring women's history through historic preservation. Dubrow, Gail Lee., Goodman, Jennifer B

Page, Max & Randall Mason (eds.). Giving Preservation a History.

Ruskin, John. The Seven Lamps of Architecture. New York: Dover Publications, 1989. Originally published, 1880.

Viollet-le-Duc, Eugène Emmanuel. The Foundations of Architecture; Selections from the Dictionnaire Raisonné. New York: George Braziller, 1990.

I will add this isn't my area of scholarly study so much as a passionate one discovered in reading so I definitely missed a few things and hope others with more experience will expound.