Short answers, pulled from the story.
The Republican Party was founded in 1854 when anti-slavery activists gathered in Ripon, Wisconsin. The party emerged as a response to the Kansas-Nebraska Act which threatened to expand slavery into western territories.
Radical Republicans were a major faction within the party from its inception in 1854 until the end of the Reconstruction Era in 1877. Thaddeus Stevens served as a leader who strongly opposed slavery and advocated for equal rights for freedmen and women.
White voters increasingly identified with the Republican Party after the 1960s following the passage of these acts. The Southern strategy appealed to many white voters disaffected by Democratic support for civil rights making Southern states more reliably Republican in presidential politics.
Ronald Reagan held office as president from 1981 to 1989 implementing conservative policies that called for reduced social government spending and regulation alongside increased military spending. His administration established Reagan-style conservatism as the prevailing ideological faction for the next thirty years until right-wing populism rose.
Donald Trump defeated Hillary Clinton in the 2016 presidential election due to narrow victories in Michigan, Pennsylvania, and Wisconsin driven by strong support among working-class white voters. His election accelerated the party's shift towards right-wing populism and decreased influence among traditional conservative factions.