1. Reconstruction (1865-1877): After the Civil War, the United States underwent a period of Reconstruction to reunite the country and address the legacy of slavery. The Reconstruction era saw the abolition of slavery, the ratification of the 13th, 14th, and 15th amendments to the Constitution, and the establishment of the Freedmen's Bureau to assist freed slaves. However, Reconstruction also faced significant challenges, including resistance from former Confederates, the rise of white supremacist groups like the Ku Klux Klan, and the Compromise of 1877 which effectively ended Reconstruction and led to the disenfranchisement of many African Americans in the South.
2. The Spanish-American War (1898): The Spanish-American War was a conflict between the United States and Spain that took place in 1898. The war was sparked by the sinking of the USS Maine in Havana harbor and the United States' desire to expand its influence in the Caribbean and the Pacific. The war resulted in a quick and decisive victory for the United States, leading to the annexation of Puerto Rico, Guam, and the Philippines, and the establishment of the United States as a major world power.
