Angered by what they see as increasing hostility toward immigrants, hundreds of thousands of people converged on City Hall Saturday to demand amnesty for illegal aliens and reject federal legislation that would build more walls along the U.S.-Mexico border. Protesters, wearing white T-shirts to symbolize peace, danced, chanted and carried large banners as they filled dozens of streets in downtown. They chanted "Mexico!" "USA!" and "Si se puede," an old Mexican-American civil rights shout that means "Yes, we can." Many protesters said lawmakers were unfairly targeting immigrants who provide a major labor pool for America's economy. The rally was organized...