NYC sets the pace.

New York City gets a lot of attention from urbanists, probably too much but it is the nation's largest city and the national media is based there so there is lots of information and the largest possible audience. Also, and this is the part that bothers me as an urbanist, there is a long standing sense that New York City is the farthest along the path that every other American city will follow. NYC is the future of other cities as they grow and age.
That perception has waned a great deal as the developing world has spawned one megacity after another that not only fails to follow the trajectory of the NYC example but also have failed to even resemble each other in any meaningful way.

But New York's status as an impressively narcissistic urban entity stuffed with excellent print media archives means that NYC is where one turns for accounts of pre-Civil War comments of city squatters. Like this...

From the New York Daily Times, July 12, 1854

Squatting is a weakness of universal humanity, and squatters are in every land a terror and a scourge. The lately civilized inhabitants of San Francisco have just passed through a series of squatter riots. The squatters engross, almost monopolize the legislation of Australia, and in some parts the great advantages secured to the United States by the new treaty with Japan, are presumed to interest, more than all others, the Squatter Sovereigns, for whom the home settlements are getting too hot.
 You think good reader, that we talk of distant lands and regions removed by continents or an ocean. Ask any owner of a vacant lot up town if he believes it. He will tell you that a squatter has his cabin on his lot, and very likely raises radishes or cabbages off his dearly-bought square feet. Nor is it easy to get possession from the intruders. They pay no rent, -they will submit to none. We heard of one simple fellow who did pay a mere nominal charge, - just enough to confess that the title was not in him, - and the consequence was that his cabin was mobbed, and he obliged to flee. They say that they are banded together to support each other in their mutual defense; that they have their lawyers to defend them when suits of ejectment are brought; that the fees are paid by taxes assessed upon each other. We have here additional reasons to pity the rich. The owners of lots, especially of lots about Yorkville, have not taxes only to pay, nor rents only to collect, nor nuisances to keep off, but these squatters to fight with, and their possession to dispute when they are ready to improve their property.

Sometimes it takes something like this to point out the obvious: anyone who breaks ranks and pays ground rent to the nominal owner needs to be forced out. This needs to be developed as an idea.

New York City, 1854