By the 1960s, the Omaha Stockyards had become the world's largest livestock processing center. They surpassed Chicago's Union Stock Yards in the late 1950s. Organized labor's hard won gains came undone as the industry restructured in the 1980s and 1990s. Improved truck and boxcar refrigeration capabilities encouraged the slaughtering process to move closer to feedlots. Plants were moved to rural areas and hired non-union labor. All centralized stockyard activity declined and the Omaha Stockyards were closed in 1999. New generations of immigrants are employed in meatpacking; now they are mostly Hispanic from Mexico, and Central and South America.