Reconstruction Era: The period following the Civil War (1865-1877) when efforts were made to rebuild and reform the United States after the abolition of slavery.
Progressive Era: A period in the late 19th and early 20th centuries marked by social activism, political reforms, and efforts to address issues related to industrialization, urbanization, and inequality.
Cold War: The geopolitical tension between the United States and Soviet Union from roughly 1947 until 1991, characterized by ideological conflicts, arms race, and proxy wars.