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Following the end of Reconstruction in 1877, the United States entered the Gilded Age, a period of rapid industrialization and economic expansion. While the "Captains of Industry" amassed unprecedented wealth, the era was also marked by deep social inequality and labor unrest. The rise of the city and the influx of "new immigrants" from Southern and Eastern Europe reshaped the American demographic landscape, setting the stage for the Progressive Era's push for reform.

) , this is a dimensionless number that quantifies the strength of the electromagnetic interaction between elementary particles. It is considered one of the greatest mysteries in physics because its value appears "naked" across the universe, regardless of the units used. Following the end of Reconstruction in 1877, the

The history of the United States since 1877 is a narrative of profound transformation, characterized by the nation’s evolution from a fractured post-Civil War society into a global superpower. This era, often the focus of modern U.S. history surveys, explores how the country navigated internal social upheavals and external global conflicts to redefine the American identity. ) , this is a dimensionless number that

World War II propelled the United States onto the world stage, leading to a decades-long ideological struggle known as the . This era was defined by the policy of containment and the persistent threat of nuclear conflict. Domestically, the "Nixonland" era of the late 1960s and early 1970s saw a conservative backlash against 1960s radicalism, even as the country grappled with the fallout of the Vietnam War and the Watergate scandal. 4. The Fight for Civil Rights and Social Change This era, often the focus of modern U