When the first buses carrying migrants from the southern border arrived in Manhattan two years ago, it seemed little more than a political stunt. If New York truly wanted to be a sanctuary city, then the Republican governor of Texas was happy to oblige by sending busloads of migrants its way.

No one could have predicted what would follow.

Just over 225,000 migrants have entered New York City since 2022. More than $6 billion has been spent on a hodgepodge of shelters that morphed into the largest system of emergency housing for migrants in the country.

Hundreds of hotels and vacant office buildings hit hard by the pandemic found second lives as converted shelters. Ball fields and warehouses were turned into barrack-style dormitories to house migrants from places including Venezuela, Peru, Morocco and Sudan.

The changes went beyond the struggle to house people. Politics changed, too. New York became embroiled in the national anger over immigration that helped Donald J. Trump recapture the presidency.

The president-elect increased his vote count in a city previously hostile to him, with the influx prompting Mayor Eric Adams, a Democrat, to reconsider one of the city’s bedrock principles: that it must provide a bed to anyone in need of shelter.