The Republican Party of the United States (also known as the Grand Old Party) was founded in 1854 by activists and modernizers particularly concerned with the anti-slavery movement. Indeed famous emancipator Abraham Lincoln was the first Republican President. They were the party of power during both the Civil War and the Reconstruction.
They were seen as a progressive party under Roosevelt in the early 20th Century but by the twenties they had become a business oriented party, a philosophy that continues up to the present day. Having presided over the Great Depression they lost power in 1932 with F.D. Roosevelt and his New Deal Coalition defeating Herbert Hoover in a landslide. Democratic presidents would oversee the Second World War and the birth of the Cold War.
The latter half of the 20th Century saw Eisenhower take the Whitehouse for the Republicans for much of the 50s, whilst in the 70s Nixon took the US out of Vietnam before disgracing himself. The 80s saw Ronald Reagan put in the groundwork for the end of the Cold War whilst in subsequent years Bush Senior and Junior put in the groundwork for the start of a new war against Islamic Terrorists.
The ideology of the Republican party is typically to the right of the Democratic Party. It is socially conservative, it is nationalist and favors libertarian economics. Recent trends include the rise of hawkish, right wing, neo-conservatives in the party and the increasing influence of Christian right-wing groups.
In the present day, Americans see the Democratic Party as the liberal option and the Republican Party as the conservative option. To foreign eyes the two parties look very similar, more like the two wings of a single center-right party. US politics, rather than being seen as a two-party system in the greatest democracy on Earth’ is seen more as a one-party state with no prospect of minority parties, who represent genuine political alternatives, such as the Green Party and the Socialist Party, having any chance of success for the foreseeable future.