Since the later 20th century, the Seneca have been increasingly active in exercising sovereignty on their reservation and enforcing their property rights. Their relations with the non-Native surrounding population have become contentious, in regard to excise tax advantages and to their property rights. In the 1990s, the Senecas won a prolonged court battle to assume ownership of all land on their reservation, including that owned by private non-Seneca.  The city had been developed under a 99-year federal lease arrangement with the Seneca Nation. It had provided land to railroads to encourage development, which the railroad developed for workers and their families, and related businesses. This arrangement was confirmed by acts of Congress in 1875, 1890 and 1990. When that lease expired in 1991, the Seneca Nation demanded that the previous owners sign new leases with their nation for not only the underlying land, but also the improvements as well, or be evicted. The Seneca evicted fifteen property owners from their homes for refusing to sign over their properties. The increase in lease revenue from this reinterpretation has generated sufficient revenue for the nation to pay its enrolled members a quarterly social dividend, providing those members with a basic income. In a similar case in 2012, the Seneca ordered an eviction of 80 residents of summer cottages at Snyder Beach on the Cattaraugus Reservation, a location near Sunset Bay. They had previously notified the owner of the land that his leases to non-Seneca were not permissible, but he had done nothing to clear his property. Some of the residents were from families who had rented there for decades. The Seneca described the non-Natives as constituting a long-standing "illegal occupation".

How many acts of Congress confirmed the 99-year federal lease arrangement with the Seneca Nation?
3